Battery help please

[WotEver]

25 minutes ago, Dr Bob said:

The BMV will be showing voltage at light load sub 12.0V

And if you don’t understand the effect on battery voltage of varying loads you will drastically miscalculate the SoC of the bank. 

 

If you do understand all of the interactions of voltage vs load then you don’t need a SmartGauge. It’s designed specifically for someone who doesn’t understand the nitty gritty and just wants a simple to understand gauge which will show with a fair degree of accuracy how full their batteries are (or aren’t!)

 

I ask again, how much personal experience do you have of using a SmartGauge? Your theoretical criticism of its function suggests very little. Nick did some interesting comparisons a few years back and found that it tracked the actual SoC well within the published figures, which is something that anyone who has used one knows already. 

 

26 minutes ago, Dr Bob said:

I think all serious boaters (ie liveaboards) should have a basic understanding of how to look after batteries.

However, what you think is irrelevant. Many boaters have no interest whatsoever in understanding the ‘nitty gritty’ and just want some simple rules to follow. The simplest rules are “charge until charge current is around 1% of capacity” plus “recharge before the batteries are down to 50%”. 

Edited June 14, 2018 by WotEver
Spurious worm

[Tony Brooks]

Bob, it is obvious that you are technically competent in your fields and also probably very intelligent. You seem to have a very good grasp of practical things as well BUT, and this is not specific to you but a far more general observation that will probably get me into trouble with the mods:-

 

Bright people have a tenancy to overestimate the capabilities of far too many. Through my years in Further Education and training and my mag work I know there are numerous people who are incapable of dealing with technical or practical operations, many who are just plain thick and many more who are just lazy and will not put the effort in. It is these people the Smartguage is targeted at and as far as I can see it does its job well enough (except in Mike's and a very few other cases).

 

I don't even have a battery monitor but use a voltmeter and ammeter but that does not mean every one can because it takes a degree of understanding of what is going, inferences to be drawn and what is to be expected.

 

I just wish the likes of the BVM etc. would acknowledge the short comings and not provide a percentage of charge display.

 

Edited June 14, 2018 by Tony Brooks

[dmr]

58 minutes ago, Dr Bob said:

The batteries do not think they are a 95%. The BMV does. As I keep saying NEVER look at SoC. The BMV will be showing voltage at rest sub 12.0V. The BMV will be showing voltage at light load sub 12.0V. If you understand that.....which should be information an 'electric only' boat owner knows....then the Smartguage is superflous. Why pay another £100 for kit that is not showing you anymore. Ok, if you dont have a battery monitor then it is a quick and easy way to get information.

As someone who understands how smartguages work, there is another issue. Voltmeters and ammeters work by reading a measured value so are accurate to the limits of accuracy and calibration on that machine. Smartguages measure voltage only -then use that voltage, the rate of change of voltage and likely the rate of change of rate of change of voltage and along with other variables calculate a SoC reading. The calculation is done via a mathematical model likely using multi linear regression. If some of the smarter modeling techniques had been used then Gibbo would have used this in the marketing bumph as Topology, neural networks, sparse data prediction etc etc are seen  by many in the industry as far better ways to predict than multi linear regression. It is difficult to get multi linear regression models to work as a 'global' model. I know. I spent 15 years managing our modelling team for a major petrochems company and sold model based prediction systems for predicting gasoline quality but using Topology. Multi linear regression just didnt hack it. Anyway, lets assume Gibbo has got a global model working .....it still means the smartguage is calculating the SoC which then brings in extra layers of potential error. We seem to understand they are not good at measuring the final stages of charge. I think I saw someone say they are not accurate below 50% which is not surprising as lots and lots of data is needed to build models and I doubt if that many of Gibbo's test data were on batteries less than 50% - so the models may not work that well below this number. Whatever you think, there will be some error and MtB has shown that just a small problem in calibration can give an expensive outcome.

I do believe smartguages are useful as they are easy to fit and no need for faffing around fitting a shunt, but unfortunately they could be expensive if you rely on the SoC output. For the same captial outlay you can buy a decent battery monitor that measures current as well and that means you can do 'your' tail current test and 'my' voltage at rest test and not bother to look at SoC. If you have a bmv already - it is a no brainer. I think all serious boaters (ie liveaboards) should have a basic understanding of how to look after batteries.

It really does not matter what modelling method the Smartgage uses, the bottom line is that it works with an acceptable accuracy during discharge which is what it's designed to do. Also although multi linear regression (whatever that is, but I assume its fitting more than one straight line to the data ?) did not work for you it might be fine for a battery which depends upon only one fairly well understood chemical reaction, and Gibbo did spend a lot of time studying battery characteristics during discharge. The error below 50% is not below 50% charge but when the capacity has fallen below 50%. A battery is at the end of its life when its down to 80% so at 50% it is totally dead and should have been replaced.

 

I believe Gibbo got the charging approximation side of things wrong. The display is optimistic whilst it should be pessimistic and its limitations during charging should have been made clearer.

 

If you search back in the forum I went through all the battery traumas of a new liveaboard boater and refused to fit a Smartgage despite forum advice because I thought it could not work on voltage only. When I eventually fitted a Smartgage (and got Trojans) then everything was sorted.   I look at the smartgage several times every day. Im going to look right now to help decide if we need an engine run this morning or if we can last till tomorrow. It also tells me when a bit of sulphation is setting in because it shows the batteries discharging faster than usual.  I use a built in ammeter to monitor charge.

 

I have also monitored state of charge from resting voltage and specific gravity and both are very tedious compared to the Smartgage.

 

I will take my batteries down to 30% once in a while if it avoids an inconvenient engine run, the Smartgage is great for keeping a close eye on this. I do not believe in the 50% rule and can find no evidence to support it.

 

..............Dave

[dmr]

59 minutes ago, WotEver said:

And if you don’t understand the effect on battery voltage of varying loads you will drastically miscalculate the SoC of the bank. 

 

If you do understand all of the interactions of voltage vs load then you don’t need a SmartGauge. It’s designed specifically for someone who doesn’t understand the nitty gritty and just wants a simple to understand gauge which will show with a fair degree of accuracy how full their batteries are (or aren’t!)

 

I ask again, how much personal experience do you have of using a SmartGauge? Your theoretical criticism of its function suggests very little. Nick did some interesting comparisons a few years back and found that it tracked the actual SoC well within the published figures, which is something that anyone who has used one knows already. 

 

However, what you think is irrelevant. Many boaters have no interest whatsoever in understanding the ‘nitty gritty’ and just want some simple rules to follow. The simplest rules are “charge until charge current is around 1% of capacity” plus “recharge before the batteries are down to 50%”. 

I disagree. I DO understand batteries (after much stress and effort over the last ten years). I have a degree in electronics and 30 years hands on experience in various aspects of engineering, I was maybe not the best manager because I preferred to do technical stuff, but then again I did not waste money on rebranding and other management hobbies. I very nearly completed a PhD in automotive electronics but went off on a more productive tangent. The Smartgage is a great instrument for anybody who uses batteries, not just for the non technical.?

 

...................Dave

[rusty69]

I love my smartgauge.

 

Mrs Rusty loves my smartguage. 

 

I like my battery monitor. 

 

Mr Rusty doesn't like my battery monitor. 

 

I like my voltmeter 

 

Mrs Rusty thinks its a digital clock. 

 

I like the fact that mtb points out that smartguages need checking. I was living in ignorant bliss until i checked mine. How many other people did though? 

[rusty69]

15 minutes ago, rusty69 said:

I like my voltmeter 

 

Mrs Rusty thinks its a digital clock

Q - "what time can i plug in my i-thingy?" 

 

A- "14.50,but not at 12.20"

Edited June 14, 2018 by rusty69

[Richard10002]

1 hour ago, WotEver said:

If you do understand all of the interactions of voltage vs load then you don’t need a SmartGauge. It’s designed specifically for someone who doesn’t understand the nitty gritty and just wants a simple to understand gauge which will show with a fair degree of accuracy how full their batteries are (or aren’t!) 

Your above sentence makes it sound like a simple fuel gauge - but it isn't, and the manual makes this clear, if you read every word on every page.

 

I believe that a Smartgauge on its own, in the hands of someone who doesnt understand the "nitty gritty", is actually quite dangerous to the state of health of their batteries... and it does not show with a fair degree of accuracy how full their batteries are, or aren't.

The manual says that the Smartgauge is not accurate above readings of 80%. Anyone who treats their batteries as full, and stops charging, when their Smartgauge reads 100%, is likely to be seriously undercharging their batteries which will sulphate and lose capacity quite quickly, (probably). My batteries are still drawing about 20A when my Smartgauge reaches 100%... My desired tail current is between 2A and 4A, which usually takes 2 or 3 more hours.

 

Smartgauge is only really useful in guiding you as to when it might be time to start charging your batteries.

 

I would modify your simple rules to accommodate the fact that you "should" charge every day to 100% where possible, and certainly no longer than 2 days.

 

The simplest rules are “charge until charge current is around 1% of capacity” plus “recharge before the batteries are down to 50%", plus, "recharge at least every second day if the batteries don't get down to 50%"”

 

I would imagine that you suggest my amendment in your post on looking after batteries, but I think it should be part of the simple rules

 

"3 Simple Rules of Good Battery Management"

 

Smartgauge helps with the second and third rules, in that it tells you that you have discharged your batteries, and by how much you have discharged when it reads below 80%. It is no use whatsoever in telling you what the charge current is, so cannot help in any way with the first bit of the rule. In addition, it is worth repeating that, on it's own, in the wrong hands, it can indicate that the batteries are full, when they are nowhere near.

 

I have had a NASA BM2 since 2012, and added a Smartgauge around 2014, (mostly out of a liking for gadgets, but also because the SOC reading of the BM2 is worse than useless). I bought 4 x Trojan T105 batteries and, effectively, followed your "simple rules", without my modification.... MtB did the same, and both of us destroyed our expensive batteries. I think we both used our batteries until they fell to around 50%, but this could take a week or so, by which time, sulphation was setting in.

 

It seems that batteries should be charged to 100% as often as possible, and certainly at intervals of no more than 2 days.

[Jeanie920]

14 hours ago, roland elsdon said:

I appreciate i am very 1980s in my technological knowledge but are you really saying that a boat with a travel power has no alternator for charging domestic batteries? So you swing a 7 kva alternator to power a  mains battery charger, and the charger cannot sense when the batts are low. If this is the case a simple flying lead from the engine start battery  with the engine running would allow sufficient voltage if needed to kick in the travelthingy. Or is the start battery on a mains charger too?

when you replace  the batts a heavy duty 120 amp alternator for domestic charging would help. Then you would use the travelthingy to do the washing and other mains only high power stuff.

 

reminds me of a screwed up new boat i was asked to look at. The batteries went flat every night after about 5 hours. The builder had saved money and chrged the bow thruster battery off a charger hidden in the front and run a mains lead under the floor. This was wired to a permenently on inverter. The bow thruster batteries were about 6 years old. All that was generated was heat and the merry sound of inverter alarms.

I disconnected the inverter and told him to go buy a shaft. Course the builder had gone broke...

No there doesn’t seem to be an alternative way to charge the batteries. When the Travel Power had to go in for repair the only way I could charge the batteries was on shore power. I don’t think there is any space for an alternator. I think we asked advice for that a couple of years ago when the TP was broken. The bow thruster has a separate battery and I have a separate starter battery. Both I assume charged via the inverters. 

[dmr]

50 minutes ago, Richard10002 said:

Your above sentence makes it sound like a simple fuel gauge - but it isn't, and the manual makes this clear, if you read every word on every page.

 

I believe that a Smartgauge on its own, in the hands of someone who doesnt understand the "nitty gritty", is actually quite dangerous to the state of health of their batteries... and it does not show with a fair degree of accuracy how full their batteries are, or aren't.

The manual says that the Smartgauge is not accurate above readings of 80%. Anyone who treats their batteries as full, and stops charging, when their Smartgauge reads 100%, is likely to be seriously undercharging their batteries which will sulphate and lose capacity quite quickly, (probably). My batteries are still drawing about 20A when my Smartgauge reaches 100%... My desired tail current is between 2A and 4A, which usually takes 2 or 3 more hours.

 

Smartgauge is only really useful in guiding you as to when it might be time to start charging your batteries.

 

I would modify your simple rules to accommodate the fact that you "should" charge every day to 100% where possible, and certainly no longer than 2 days.

 

The simplest rules are “charge until charge current is around 1% of capacity” plus “recharge before the batteries are down to 50%", plus, "recharge at least every second day if the batteries don't get down to 50%"”

 

I would imagine that you suggest my amendment in your post on looking after batteries, but I think it should be part of the simple rules

 

"3 Simple Rules of Good Battery Management"

 

Smartgauge helps with the second and third rules, in that it tells you that you have discharged your batteries, and by how much you have discharged when it reads below 80%. It is no use whatsoever in telling you what the charge current is, so cannot help in any way with the first bit of the rule. In addition, it is worth repeating that, on it's own, in the wrong hands, it can indicate that the batteries are full, when they are nowhere near.

 

I have had a NASA BM2 since 2012, and added a Smartgauge around 2014, (mostly out of a liking for gadgets, but also because the SOC reading of the BM2 is worse than useless). I bought 4 x Trojan T105 batteries and, effectively, followed your "simple rules", without my modification.... MtB did the same, and both of us destroyed our expensive batteries. I think we both used our batteries until they fell to around 50%, but this could take a week or so, by which time, sulphation was setting in.

 

It seems that batteries should be charged to 100% as often as possible, and certainly at intervals of no more than 2 days.

I also observe over 20 amps going in when the Smartgage says 100%, but I do have 6 Trojans and two are getting on a bit (mixing old and new in the same bank!!!!) which is why I said that I think Gibbo got the charging display wrong, BUT Smartgage really is a device to give state of charge during discharge.

 

I keep saying again and again, the old wisdom was to charge to about 80% every day and to 100% once a week. If you are engine or genny charging then charging to 100% every day is a waste of fuel. This new forum wisdom of constant charging to 100% is WRONG. Due to laziness and other things I recently failed to get mine up to 100% for over a month. I did think we might have blown it this time but a good charge and a little equalisation looks to have got them back on form, however these are Trojans and it might be different with cheapo stuff.  The issue is not charging to 100% everyday but having the ability to set a voltage such that you can fully charge the batteries to a real proper 100% when you do charge them, this will likely include a bit of equalisation if you have left it a bit long..

 

...............Dave

[Jeanie920]

14 hours ago, dmr said:

ave heard of other boats with only a TravelPower and no domestic alternator, but I would expect a starter alternator as otherwise you really have got all your eggs in the TP basket. I think the big 7kW TP is actually two 3.5kW TPs rolled together in the same box so the OP already sort of has a dedicated charging system separate from the washing machine. I think the TP could be driven from the starter battery but not sure if there is any current draw when its turned off. A flying lead or alternator shorting relay would fix the charger start up issue but that's neither here nor there 'cus the batteries really should Never be allow to get to such a low state of charge.

Yes I should have replaced the batteries before we set off on our journey. We could then have done the leisurely journey that we planned and not the must get there as soon as possible journey that we did.  Now at least I have a better understanding that it’s the volts I should be looking at and not the SoC. 

I think the 7kw Travel power is not two 3.5. When we had trouble with the TP someone from Leek who specialises in TP came to look and said he couldn’t touch it as he could only do 3.5 TPs. I asked him was it not just a bigger version and he said they were completely different. 

I know I need new batteries but what I really would like to know is can I replace these Victron 12-200 gel batteries with a cheaper make of the same size. AGM seem to be a cheaper alternative to gel. Could I use those?

3 hours ago, system 4-50 said:

Probably a silly question but are all the batteries wired together as one bank or is there a pair for each combi?

There are 5 batteries all wired together 

[WotEver]

1 hour ago, Richard10002 said:

The manual says that the Smartgauge is not accurate above readings of 80%

No it doesn’t!  Where on earth did you invent that from?

 

Absolute rubbish. 

[WotEver]

1 hour ago, dmr said:

The Smartgage is a great instrument for anybody who uses batteries, not just for the non technical.?

I agree, I think it’s great to simply glance at a gauge in the morning (or evening) and see where your batts are at. 

[dmr]

19 minutes ago, Jeanie920 said:

Yes I should have replaced the batteries before we set off on our journey. We could then have done the leisurely journey that we planned and not the must get there as soon as possible journey that we did.  Now at least I have a better understanding that it’s the volts I should be looking at and not the SoC. 

I think the 7kw Travel power is not two 3.5. When we had trouble with the TP someone from Leek who specialises in TP came to look and said he couldn’t touch it as he could only do 3.5 TPs. I asked him was it not just a bigger version and he said they were completely different. 

I know I need new batteries but what I really would like to know is can I replace these Victron 12-200 gel batteries with a cheaper make of the same size. AGM seem to be a cheaper alternative to gel. Could I use those?

There are 5 batteries all wired together 

Victron are generally seen as expensive so a non-brand battery might well be cheaper and possibly just as good. I have no experience of AGM and gel so can't advise, I'm one of those sad gits who almost enjoys topping up batteries with distilled water.

 

I do suspect that your all electric lifestyle is going to be electrically difficult so it might be wise to get the cheapest batteries that you can find and just accept that they will need replacing frequently.

 

.............Dave

[WotEver]

1 hour ago, Richard10002 said:

I believe that a Smartgauge on its own...

Which is not something that I have suggested at any point in this thread. You should ideally couple it with (at the very least) an ammeter. 

 

ETA: I didn’t suggest that OP fits an ammeter because she already has a BMV, so a SmartGauge would be an ideal companion to that. She now says she’ll monitor voltage without any apparent understanding of what voltage she should be looking at under what circumstances, so it’ll still end in tears. 

Edited June 14, 2018 by WotEver

[Jeanie920]

6 minutes ago, WotEver said:

I agree, I think it’s great to simply glance at a gauge in the morning (or evening) and see where your batts are at. 

But you can do that with the BMV. Mine is above my cooker so it’s very accessible at all times. I now know it’s the volts I should be looking at so I can set the default mode to read volts and not SoC. 

[WotEver]

Just now, Jeanie920 said:

But you can do that with the BMV

No you can’t, because it tells lies if you’re looking at SoC, and the voltage is meaningless unless you have removed the surface charge from the batteries and turned absolutely everything off. Compare that to a display that will instantaneously tell you in the middle of the evening that your batteries are down to 55%. 

39 minutes ago, dmr said:

Smartgage really is a device to give state of charge during discharge.

Precisely. Its best use is in letting you know in advance that you really ought to start turning stuff off or, if between 8-8, start charging. 

[MtB]

Now I have manually re-calibrated my Smartgauge I find it works very well. Even with my sulphated battery bank which is probably well below 50% of badge capacity.

 

It has however, two rather nasty traps for the unwary, both of which I fell into.

 

1) It misleads you during charging. It says 100% SoC when the batteries are nothing like fully charged.

 

Granted it tells you this in the manual (on Page 28!), but the device would be greatly improved if during charging the display stopped showing an incorrect SoC, changing instead to displaying a C for 'charging'. Or anything other than a lie about the actual SoC. I missed the comment on Page 28 telling me the SoC displayed during charging was wrong and wrecked . £400 set of batteries as a result.

 

2) They cannot be trusted to be correctly calibrated straight from the box. After I sussed what it says on Page 28, my batteries still seemed to be degrading. On checking the calibration of my sSartgauge it turned out to be grossly over-stating the SoC even during discharge. When my rested battery voltage was down to 12.0v, the Smartgauge was telling me 70% SoC when the true value was closer to 40%. Not good for an instrument designed to do nothing other than tell you the SoC. 

 

Of the few people on here who have taken the trouble to check the accuracy of their Smartgauges, five (I think) have been found to be wrong. 

 

If these two issues can be fixed (i.e. stop displaying a false SoC during charging, and send them out form the factory accurately calibrated) the Smartgauge would be a really nice piece of kit in my opinion.

[ditchcrawler]

15 hours ago, roland elsdon said:

I have a plug in cigar socket voltmeter at one endof the line in the back cabin and a $15 digital voltmeter in the living kitchen bedroom music room library bathroom . (10 foot extension) im rarely out of sight of the voltmeter. If it goes below 12.2 with the fridge compressor on i turn off the fridge and go to bed.

high tech monitoring. 

But are you fully recharging them the next day?

 

[WotEver]

33 minutes ago, Mike the Boilerman said:

send them out form the factory accurately calibrated...

This is kinda fundamental for a device that uses the measured voltage to function. If you find that another new one is uncalibrated then I’ll join you in dissing them

 

8 minutes ago, ditchcrawler said:

But are you fully recharging them the next day?

And how would you know?

Edited June 14, 2018 by WotEver
Tryping

[dmr]

24 minutes ago, Mike the Boilerman said:

Now I have manually re-calibrated my Smartgauge I find it works very well. Even with my sulphated battery bank which is probably well below 50% of badge capacity.

 

It has however, two rather nasty traps for the unwary, both of which I fell into.

 

1) It misleads you during charging. It says 100% SoC when the batteries are nothing like fully charged.

 

Granted it tells you this in the manual (on Page 28!), but the device would be greatly improved if during charging the display stopped showing an incorrect SoC, changing instead to displaying a C for 'charging'. Or anything other than a lie about the actual SoC. I missed the comment on Page 28 telling me the SoC displayed during charging was wrong and wrecked . £400 set of batteries as a result.

 

2) They cannot be trusted to be correctly calibrated straight from the box. After I sussed what it says on Page 28, my batteries still seemed to be degrading. On checking the calibration of my sSartgauge it turned out to be grossly over-stating the SoC even during discharge. When my rested battery voltage was down to 12.0v, the Smartgauge was telling me 70% SoC when the true value was closer to 40%. Not good for an instrument designed to do nothing other than tell you the SoC. 

 

Of the few people on here who have taken the trouble to check the accuracy of their Smartgauges, five (I think) have been found to be wrong. 

 

If these two issues can be fixed (i.e. stop displaying a false SoC during charging, and send them out form the factory accurately calibrated) the Smartgauge would be a really nice piece of kit in my opinion.

It's an old design, sold to another company, and so likely just bringing in a small income with minimal effort. I guess the jargon is end of the product lifecyle. This might even be why the factory calibration went wrong. A lot of people think its an old fashioned looking design though I rather like the way it looks, so I doubt there are any plans to re-work it as it would need more than just a software upgrade. In fact I do suspect the Gibbo produced it as a labour of love rather than a big money making enterprise. Times have moved  on, there are Chinese amp-hour counters on eBay for almost nothing so the chances of getting the money back on a rework are slim.

 

The device from  Simarine that has a shunt and claims a Smartgage type algorithm looked very promising but had some issues that are possibly not getting sorted out.

Any feedback from the forum member(s) who got one????

 

..............Dave

[MtB]

2 minutes ago, WotEver said:

This is kinda fundamental for a device that uses the measured voltage to function. If you find that another new one is uncalibrated then I’ll join you in dissing them

 

 

I have two wrongly calibrated, Rusty has one, and there are a couple of others on here too. 

 

How many more do you want?!

 

 

[MtB]

2 minutes ago, dmr said:

It's an old design, sold to another company, and so likely just bringing in a small income with minimal effort. I guess the jargon is end of the product lifecyle. This might even be why the factory calibration went wrong. A lot of people think its an old fashioned looking design though I rather like the way it looks, so I doubt there are any plans to re-work it as it would need more than just a software upgrade. In fact I do suspect the Gibbo produced it as a labour of love rather than a big money making enterprise. Times have moved  on, there are Chinese amp-hour counters on eBay for almost nothing so the chances of getting the money back on a rework are slim.

 

I think you are right about all of this. The appearance of the device leads the workers on the shop floor churning them out to view them as old hat and not worth taking much trouble over. 

 

If and when the Smartgauge production stops, and I can't see that being too long now, the second hand value of them will rocket as they will acquire cult status. Nothing else does the job they do quite so well once the user has calibrated theirs accurately, and properly grasped that the SoC display during charging MUST BE IGNORED.

[Iain_S]

16 hours ago, Mike the Boilerman said:

 

So what does the team think these "new battery testers" are actually measuring? Just terminal voltage would be my guess. 

(snip)

Terminal voltage, voltage drop on a fairly hefty discharge, plus recovery time after discharge would be my guess. 

[Dr Bob]

1 hour ago, WotEver said:

No you can’t, because it tells lies if you’re looking at SoC, and the voltage is meaningless unless you have removed the surface charge from the batteries and turned absolutely everything off.

I am sorry Tony but that is bad advice. Of course the voltage is not meaningless if you do not have absolutely everything turned off. The smartgauge works it out! In the early morning before the solar kicks in, I look at my bmv. The inverter is running with a bit of stuff (chargers etc). Typically 1.7A draw. If the fridge compressor running then 5.4A draw. I know from just a weeks experience that the 1.7A draw means the voltage is approx 0.1V less than the true at rest voltage. You can estimate. I agree you cannot do much with surface charge but you can also look at the amphrs used if you need a ball park........and there is not likely to be a surface charge if you are looking if the voltage is too low.

This is not difficult science as Tony B suggested. Anyone who can grill a decent Rump steak (timing, visual assessment etc) can learn to recognise the important battery stuff. Jeanie should be able to eyeball her bmv and understand what the voltage is telling her with the amps and/or amp hours without spending another £100.

If you are not capable of the basic understanding then maybe a smartgauge will give you a 'fuel gauge' but beware the problems of relying on it as highlighted by MtB and Richard.

My contention is that if you know enough to use a bmv (or Nasa or equiv) to a reasonable level then the smartgauge tells you little more so they dont really compliment each other. If you cant understand a bmv then get a smartgauge or learn how to cook steaks.

[Dr Bob]

4 hours ago, WotEver said:

However, what you think is irrelevant. Many boaters have no interest whatsoever in understanding the ‘nitty gritty’ and just want some simple rules to follow. The simplest rules are “charge until charge current is around 1% of capacity” plus “recharge before the batteries are down to 50%”. 

Absolutely. Excactly what I mean about serious boaters understanding how to look after their batteries. Follow your simplest rules.

You can do this with a basic knowledge of a BMV. They cannot follow your simple rules with only a smartgauge.