Battery charge question

[Boat afloat]

We’re experiencing a little annoyance on our boat in that by evening the leisure batteries appear to be tired.

 

we have 5 leisure’s plus 2 solar panels but by 10pm the laptop and router will quietly retire for the evening.

 

there is a little voltmeter in the boat which always seems to read pessimistically. After cruising it will read 12.6 and slowly drain to 11.5 at which point the 12v sockets stop working.

 

some points then:

- everything seems to be charging when the engine is running

- the solar has been reset and tends to run at 12.6 - 13.4 so seems to be doing it’s bit…?

- if I stick a multimeter on the leisure batteries  individually after running I get 12.6-13v each APART from the one closest to the cabin which always says 11.6 regardless of running

- the weak battery is only connected to the other 4 via the negative terminal (?)

- if I disconnect the negative terminal of the weak battery and therefore presumably take it out of play (?) nothing seems to change

- our inverter is a small one but does that matter because we aren’t power hungry?

 

I’ve been through the boat to turn everything off that could be draining things but wonder what it could be? My focus has been on the weak battery and the inverter but maybe I’m missing something? The fact the batteries themselves seem to be at healthy voltages is foxing me a little…

 

anyway, I thought I’d post up for some practical help and assistance because I’m sure there’s knowledge out there which can help.

 

cheers

 

 

[Rob-M]

Your batteries sound like they are knackered.  Although they may charge it sounds like they no longer have anything like the original capacity so quickly discharge.

 

How long are you charging for and does the solar ever take them up to something more like 14.5v...?

[Naughty Cal]

It sounds like you are never fully charging your batteries.

 

At 12.6v on charge they are a long way from full.

 

Letting them drop in voltage to the point where things turn off won't have done them any favours either. They are probably knackered by now.

 

Get a fresh set of batteries and learn how to look after them before you trash them as well.

[Rambling Boater]

How old are the batteries? Are you always off grid (i e never connect to a shore line).

[David Mack]

59 minutes ago, Boat afloat said:

the weak battery is only connected to the other 4 via the negative terminal (?)

So what is the positive terminal connected to? Nothing? If so this battery is not in circuit and is therefore not being charged or discharged.

[nicknorman]

10 minutes ago, David Mack said:

So what is the positive terminal connected to? Nothing? If so this battery is not in circuit and is therefore not being charged or discharged.

Maybe it is in fact the starter battery?

 

Anyway none of the charge voltages mentioned sound remotely high enough. Before splashing out on new batteries, check to see that you are getting 14.4v or so with the engine running after a day’s cruising. If you don’t get that sort of voltage, something is wrong with the alternator/charging system and this should be sorted out before buying new batteries.

[Tony1]

 

You are right and there are a few very helpful people here who are genuine experts in how to manage batteries (and sadly I'm not one of them), so you will get the advice you need in understanding what's going on.

 

When I first got my boat I found a similar thing- in my case after a 7 hour cruise with added solar, the battery voltage would increase to 14v and beyond, which seemed to indicate that they had a fairly high state of charge. 

The problem was that their capacity to hold charge was greatly reduced over the years. They were officially rated at 300Ah in total, but by 10pm the voltage had dropped to 12.2v, which I believe indicates that they are down to around 50% charged (which as low as you want them to go). 

I reckoned I used about 30-40Ah by the time they got down to 12.2v/50% SoC, so my guess was that they probably had a combined capacity of about 80Ah at most.

 

If you are letting your batteries get down to 11.5v on an almost daily basis, its possible they are already damaged, but it might help if you add a bit more info about how old they are, and what your normal charging routine is, so that the experts here can get a feel for the likelihood of them being damaged/knackered.

 

 

[Tracy D'arth]

Did you ever do an energy audit?

Is there an inverter powered up all the time?

12v fridge and TV?

[PeterF]

Read the battery charging primer for key information on charging batteries.

Battery charging primer

[MtB]

3 hours ago, Boat afloat said:

After cruising it will read 12.6

 

As Nick pointed out, this is the root problem. It should be reading 14.4v or even more. 

 

Whatever battery or batteries the voltmeter is connected to, it/they are not getting charged properly. Fix this fault first or any new batteries you buy will go the same way in a few weeks.

 

Top reasons for the charging voltage being too low are:

 

1) Vee belt too loose

2) Poor electrical connection (or connections) in the charging circuit

3) Diode failed in alternator

4) High power drain on the batts exceeding the charging input. 

 

Edit to add:

Oops misread the bit I quoted! 12.6v is just about ok after cruising. But what is the voltage during cruising? Needs to be 14.4 or higher.

 

 

Edited April 16, 2022 by MtB

[Boat afloat]

1 hour ago, MtB said:

 

As Nick pointed out, this is the root problem. It should be reading 14.4v or even more. 

 

Whatever battery or batteries the voltmeter is connected to, it/they are not getting charged properly. Fix this fault first or any new batteries you buy will go the same way in a few weeks.

 

Top reasons for the charging voltage being too low are:

 

1) Vee belt too loose

2) Poor electrical connection (or connections) in the charging circuit

3) Diode failed in alternator

4) High power drain on the batts exceeding the charging input. 

 

Edit to add:

Oops misread the bit I quoted! 12.6v is just about ok after cruising. But what is the voltage during cruising? Needs to be 14.4 or higher.

 

 

Thanks for all the replies so far.

 

Up until a week or so ago the boat was on a shoreline. Since then the boat has been moving.

 

During cruising I think the voltage rises to the 13's but not the 14's. We are back at the boat again in a few days so I can check, BUT even if the boat is only charging in the 13's surely we could expect the batteries to hold out longer than they are...they seem to be draining even under super light use (router plugged in and not much else).

 

I agree that checking the charging system seems to be the thing here...

 

Regards the previous question about what the 'weak' battery is connected to the positive connector isn't connected to the other batteries, just the negative so it looks like that battery has been taken out of the system entirely.

 

Question: When batteries are connected in the way they are on a boat if one fails is it usual to have them all go?

[Rob-M]

You need to be charging over 14v, our alternator only gets to 14.1v but our solar charges at 14.5v.  This also depends on your battery type, we haved sealed LAs so don't want to go too high and have them gassing 

[Richard10002]

4 minutes ago, Boat afloat said:

During cruising I think the voltage rises to the 13's but not the 14's.

 

How are you measuring this. You need to do it with a meter at the batteries, or a specialist battery monitor, e.g. NASA BM1, Victron BMV712, etc.

 

 

4 minutes ago, Boat afloat said:

Regards the previous question about what the 'weak' battery is connected to the positive connector isn't connected to the other batteries, just the negative 

 

You seem to be saying that the positive terminal is bare? Is there a wire connected to the positive terminal of this battery? If so where does it go? A photo of your batteries might help.

[Alan de Enfield]

30 minutes ago, Boat afloat said:

During cruising I think the voltage rises to the 13's but not the 14's. We are back at the boat again in a few days so I can check, BUT even if the boat is only charging in the 13's surely we could expect the batteries to hold out longer than they are...they seem to be draining even under super light use (router plugged in and not much else).

 

 

Simply - if you do not get the batteries recharged to 99.99% every few days the batteries start to sulphate - this is a sort of lead-mud and it builds up in the battery.

 

I use this as an analogy.

 

You have a 100Ah battery this is the amount of energy it can store.

 

You have a 5 litre bucket, this is the amount of water it can hold.

If you put a couple of inches of mud in the bottom of the bucket it remains 'a 5 litre bucket' but it is now only capable of holding 4.5 litre.

If you add another couple of inches of mud in the bottom of the bucket it remains 'a 5 litre bucket' but it is now only capable of holding 4 litre.

If you add another couple of inches of mud in the bottom of the bucket it remains 'a 5 litre bucket' but it is now only capable of holding 3.5 litre.

Ad infinitum

 

The same with your battery - unless it is fully recharged every time it is used (ideally daily but that is not really practical) the 'mud' continues to form and you end up with (say) a 20Ah battery.

 

If the battery, when new, would power your electics for (say) 5 hours, it now can only manage 1 hour.

 

Do not confuse volts and amps - it is amps that 'power' your appliances.

You can have a 12 volt battery the size of a finger nail, or the size of a bus, or anywhere in between  - all are 12 volts but the smaller it is the less Ah (amp hours) it will hold.

Edited April 16, 2022 by Alan de Enfield

[MtB]

There have been a couple of threads recently where people have had their batts on long term float, then gone out for a cruise and found the previously satisfactory battery bank as good as useless. Its not supposed to happen this way but it looks to me as though batts on long term float sulfate up just like partially charged batts. 

[Alan de Enfield]

1 minute ago, MtB said:

There have been a couple of threads recently where people have had their batts on long term float, then gone out for a cruise and found the previously satisfactory battery bank as good as useless. Its not supposed to happen this way but it looks to me as though batts on long term float sulfate up just like partially charged batts. 

 

I wonder .................

 

Maybe there is something in that, as you say,recently quite a few examples of folks having been on Hook-up (for Winter ?) and then go out and after the 1st couple of days find the batteries no longer do what they did last Autumn.

[MtB]

2 minutes ago, Alan de Enfield said:

 

I wonder .................

 

Maybe there is something in that, as you say,recently quite a few examples of folks having been on Hook-up (for Winter ?) and then go out and after the 1st couple of days find the batteries no longer do what they did last Autumn.

 

 

There are several ways in which LA batts don't always behave as per received wisdom. Another example is my own set of leisures that discharged down to 0.1V when the heater plug relay jammed ON and I didn't notice. I was away from the boat for about ten days and had left the 1/2/both battery selector in 'both', so when I cam back the batts ought to have been totally fkuced. But they weren't. I just charged them all up and they've been fine for the subsequent two years. No noticeable difference in performance. (Not particularly expensive Hankooks, by the way.)

[Tracy D'arth]

1 hour ago, Boat afloat said:

Thanks for all the replies so far.

 

Up until a week or so ago the boat was on a shoreline. Since then the boat has been moving.

 

During cruising I think the voltage rises to the 13's but not the 14's. We are back at the boat again in a few days so I can check, BUT even if the boat is only charging in the 13's surely we could expect the batteries to hold out longer than they are...they seem to be draining even under super light use (router plugged in and not much else).

 

I agree that checking the charging system seems to be the thing here...

 

Regards the previous question about what the 'weak' battery is connected to the positive connector isn't connected to the other batteries, just the negative so it looks like that battery has been taken out of the system entirely.

 

Question: When batteries are connected in the way they are on a boat if one fails is it usual to have them all go?

Is that router 12v? Or do you have an inverter running 24/7 to power it?  What is not much else? Its all a drain on the batteries.

Do an energy audit. It cheaper than destroying batteries through ignorance.

[Boat afloat]

1 hour ago, Richard10002 said:

 

How are you measuring this. You need to do it with a meter at the batteries, or a specialist battery monitor, e.g. NASA BM1, Victron BMV712, etc.

 

 

 

You seem to be saying that the positive terminal is bare? Is there a wire connected to the positive terminal of this battery? If so where does it go? A photo of your batteries might help.

Yes, to be fair the 13 point something volts reading is from the digital meter in the boat, which I think is pessimistic. I'll get a proper reading from the batteries themselves when running - good plan!!

 

Yes, the positive terminal of the 5th battery is bare. I've attached a picture of what I am trying to describe. I'm not with the boat to take pics unfortunately.

 

In terms of other points:

 

- the router is a 240v jobbie running through the inverter yes.

 

- when I say very little else running I really mean it. Unless it's something hidden in the boat, or the inverter is just drawing huge power I can't see what else is doing it.

 

- regards my comment about the batteries settling at 12.6v resting charge after a cruise that should be fine shouldn't it? Should I be expecting much more than that?

 

- the solar is set to cut off at 14.5V IIRC.

 

55 minutes ago, Alan de Enfield said:

 

 

I use this as an analogy.

 

You have a 100Ah battery this is the amount of energy it can store.

 

You have a 5 litre bucket, this is the amount of water it can hold.

If you put a couple of inches of mud in the bottom of the bucket it remains 'a 5 litre bucket' but it is now only capable of holding 4.5 litre.

 

That's a great analogy - I'll remember that one.

[Alan de Enfield]

8 minutes ago, Boat afloat said:

regards my comment about the batteries settling at 12.6v resting charge after a cruise that should be fine shouldn't it? Should I be expecting much more than that?

 

Is that 12.6v after 2 hours with nothing going in and nothing coming out, ie 'rested voltage' with time allowed for the absorbtion of the surface voltage effect ?

 

If you are only ever getting to 12.6 volts then you are never getting above 90% state of charge. You will be 'sulphating' the batteries more and more every day.

 

12.7v-12.8v is normally considered to be 100%

 

It could take as much as 4 or 5 hours of engine running to get from 90% to 100%. Do not think that if you have a (say) 70 amp alternator that it puts in 70 amps - as the battery gets to 90% it could be only putting in 5 amps or 10 amps or..... (depending)

 

 

Edited April 16, 2022 by Alan de Enfield

[Tracy D'arth]

So how much current do you think your inverter uses in a day doing  "not much"? You will be surprised if you actually bother to measure it. 

[Boat afloat]

11 minutes ago, Tracy D'arth said:

So how much current do you think your inverter uses in a day doing  "not much"? You will be surprised if you actually bother to measure it. 

It's an interesting point. My gut reaction would be to say for 90% of the time it's running in conjunction with the engine but thinking about it we haven't turned it off at night. That's something to definitely start doing actually because we have battery operated lighting for the evening.

 

I still think 'something' is going on whether it's in excessive draw somewhere, poor recharging or tired batteries.

 

an energy audit is to systematically test the batteries voltage with certain usage behaviour is it and see what's happening to the juice?

[Alan de Enfield]

13 minutes ago, Boat afloat said:

- the router is a 240v jobbie running through the inverter yes.

 

To follow up on Tracy's point - what make and model is you inverter ?

It is not unknown for a 'cheapy' inverter, even a Sterling to take 4Ah (thats 100ah or two batteries, discharged to 50%, worth per day)and that is just the quiescent current that it uses to power itself.

 

As a comparison my 12v fridge takes around 30Ah per day - less than 1/3rd of some inverters just on 'standby'.

 

You need to know what equipment you have and how much it uses - it is called a 'power audit' (mentioned earlier in the thread) You really need to do one and compare your demands with you capability of replacing that used, allowing an additional 20% to allow for losses.

So, if for example you find you are using 100Ah per day, you need to ensure you can generate at least 120Ah by whatever means - Solar, engine alternator, generator or battery charger on a land-line.

Just now, Boat afloat said:

an energy audit is to systematically test the batteries voltage with certain usage behaviour is it and see what's happening to the juice?

 

 

NO NO NO>

Forget voltage it is current (amps) you need to count.

[Tony Brooks]

48 minutes ago, Alan de Enfield said:

 

I wonder .................

 

Maybe there is something in that, as you say,recently quite a few examples of folks having been on Hook-up (for Winter ?) and then go out and after the 1st couple of days find the batteries no longer do what they did last Autumn.

 

I too have had similar thoughts but if it were sufation  I would expect a lot more instances and from those with solar charging as well as shoreline. I have two thoughts, could it acid stratification so only part of the plates react properly or could it be that over the winter a cell or cells have developed partial internal shorts. That would look like a loss of capacity to many boaters unless they were monitring the time taken to fully charge and the time taken to discharge (sulfation = fast recharging & fast dischargng. Intermal shorts = long time recharging and fast discharging).

 

I wonder if that last battery had been disconnected because it was self discharging and pulling the rest of the bank down.

[MtB]

4 minutes ago, Alan de Enfield said:

It is not unknown for a 'cheapy' inverter, even a Sterling to take 4Ah

 

First thing the OP needs to do is get up to speed on the difference between volts and amps. And then the difference between amps and amphours.

 

Then he'll be able to spot your deliberate mistake!