Leisure batteries and capacities

[kalees]

Hi all,

 

I am looking to replace my leisure batteries as I  would like more capacity. I currently have 2 105ah and would like to know if there would be any advantage to using 3 smaller ah or 2 larger ah to reach around 400ah, 2 would be easier due to space available?

 

for info, my only charge source is a single 100 amp alternator for the starter, bow thruster and leisure batteries, not sure if this has any impact on the way to proceed.

[Alan de Enfield]

Why do you need more capacity ? 

 

You need to do an electrical audit of your usage, you then need to balance your capacity with your usage, AND then balance that with your charging ability.

 

If you do not have enough charging capability then you will not get your new batteries properly charged and they will quickly lose their capacity.

 

You canot just randomly change things. it is a SYSTEM and each thing is interlinked and must be balanced with the others 

 

Charging (alternator) - Storage (batteries) - Usage (Discharge) - Charging - Storage -  etc etc etc

[Machpoint005]

The OP doesn't say whether his batteries are knackered. If they are OK, then the old oil industry adage shoud apply:

 

If it ain't broke, don't fix it!

[Idle Days]

To try and answer the OP's question. I don't think there is any great advantage in changing the number of batteries. Smaller units will be a little lighter, whilst fewer units should be a little cheaper. 

 

Doubling the capacity is a big step and as others have said of little advantage if they cannot be correctly charged and maintained. 

[Bee]

Depends on many things, if you only have a bit of extra space you probably can't make much difference anyway.  A lot depends on your charging really. If we are charging off the engine the 2 x 110 ah batts are 'full' after about 4 hours - this is very un scientific -  4 hours is about what we do most days so we cannot charge another batt. unless we run the engine another couple of hours. However we do have a solar panel so on sunny days and 4 hours cruising we could 'fill' a bit more batt. capacity. We also often tie where there is electric, this is in France where electric hook up is more common so we could charge another 110 ah battery but adding that last battery means 3 half charged batteries most days unless we increase the alternator size........ and so on. You can only get out what you put in and 2 batteries will last maybe 3 years, 3 batteries will also last maybe 3 years and cost more to replace.

[David Mack]

6 minutes ago, Bee said:

If we are charging off the engine the 2 x 110 ah batts are 'full' after about 4 hours - this is very un scientific -  4 hours is about what we do most days so we cannot charge another batt. unless we run the engine another couple of hours. 

Not so. The charging current is determined by what the batteries will take, and for most of the time the alternator is putting out less than its stated maximum output. So if you add an extra battery, with it's own charging current demand, the alternator will be able to provide that with little or no increase in the overall charging time.

[Tony Brooks]

I note Alan's question is yet to answered. This means we have no idea if the OP has a problem, and if so what the problem is. My guess would be they have constant battery problems because their electrical demands and ability to recharge properly are way out of step.

 

My advice is to forget Bes's four hours. On a tolerably well-designed for its use system that will get you to about 80% charge. The other 20% will take at least another 4 to 6 hours. Sometimes more. The do the power audit and charging calcs, as Alan suggested.

 

The OP, I hope, grasps that the deeper the discharge and the longer that discharge is left the more and more battery capacity they will destroy. Simply adding more capacity without addressing the ability to properly recharge it is just wasting money.

 

 

[kalees]

Hi all,

 

The reason for the question is that I suspect that the batteries need to be replaced and I was looking at this as an opportunity to provide us with some extra capacity. In terms of usage, I have an amp meter on the boat which shows the fridge drawing about 4 amps and the Webasto, when in use, another 4 amps. At the moment, beyond the charging of phones .01 amp and the inverter when on stands idle at 1 amp we currently use very little other power.

 

Looking forward, we are looking to spend a lot more time on the boat and may introduce a TV 12 or 240 V to be decided and the occasional charging of a Chromebook which takes 4 amps and will likely be looking to moor up for 3-4 days at a time and envisage a typical cruising day to be about 5 hrs.

 

As mentioned, we currently only have aa single 100 amp alternator and no solar.

 

AMG deep cycle batteries have been suggested.

[Alan de Enfield]

2 minutes ago, kalees said:

The reason for the question is that I suspect that the batteries need to be replaced

 

Why, what tells you they need replacing ?

 

 

2 minutes ago, kalees said:

Looking forward, we are looking to spend a lot more time on the boat and may introduce a TV 12 or 240 V to be decided and the occasional charging of a Chromebook which takes 4 amps and will likely be looking to moor up for 3-4 days at a time and envisage a typical cruising day to be about 5 hrs.

 

Please try and understand that you cannot take out what you haven't put in. You cannot just add an extra battery without ensuring the rest of the 'circle' is compatible.

 

You are unlikely to be able to stop for 3 or 4 days without running the engine for several hours per day, and (maybe) 8 hours at the weekends.

 

The 'average' canal boater (is there such a thing) uses about 100Ah per day, so you need to relace about 120Ah per day to maximise your battery life.

AND please do not think that your 100 amp alternator will put in 100A in one hour.It doesnt work like that.

[Tony Brooks]

You will find it difficult to test AGM or any other sealed batteries yourself. I would go open cell every time.

 

I don't think that you have grasped the consumption thing. The fridge may draw 4 amps but how long is it on for?  That is difficult to answer because its thermostatically controlled so on and off all the time but we usually reckon on 35 to 50 Ah per day. The Webasto is similar but in winter probably runs for longer so at last another 50Ah per day. You have 210 Ah of battery capacity, assuming new batteries without any sulphate. It will actually be less or far less than that. For optimum life its generally held it is not good to discharge below 50% so the fridge and Webasto may well be using all the battery capacity. Anything else you use just discharges them even deeper.

 

% hours a day cruising is unlikely to get your batteries fully charged, maybe 80%, if you are lucky, but not after 3 to 4 day without any other charging.

 

Edited to add; take notice of what Alan said about the alternator. Providing the engine is running fast enough, you will probably get about half its rated output over 3 hours or so. From then on the average goes down and  down until for the last few hours it may only be charging at about 2 or 3 amps.

Please do the proper and careful calculations and I doubt your wish for 3 to 4 days without charging is remotely possible, but may e if you install a lot of solar charging. I am convinced just one extra battery will not do the job unless you sort out how they are to be fully charged.

Edited June 20, 2021 by Tony Brooks

[David Mack]

1 hour ago, kalees said:

 

As mentioned, we currently only have aa single 100 amp alternator and no solar.

Single 100A alternator is fine. The issue is not what maximum output it has, since it will only be producing the full output for a short time. The issue is, as others have said, whether you charge long enough to get the last few Ah into the batteries to stop them deteriorsting. 

Get some solar. Even a single panel will top up the batteries whenever the sun shines, whether you are on board or not. So the batteries will be fully charged when you arrive at the boat, and you stand much more chance of keeping them that way with a limited number of hours boating. And solar is particularly good for the long periods at low charge rates needed for final charging. At this time of year you could be getting some charging for 16 hours a day.

4 hours ago, Alan de Enfield said:

Why do you need more capacity ? 

 

You need to do an electrical audit of your usage, you then need to balance your capacity with your usage, AND then balance that with your charging ability.

 

If you do not have enough charging capability then you will not get your new batteries properly charged and they will quickly lose their capacity.

 

You canot just randomly change things. it is a SYSTEM and each thing is interlinked and must be balanced with the others 

 

Charging (alternator) - Storage (batteries) - Usage (Discharge) - Charging - Storage -  etc etc etc

How many boatbuilders do an energy audit? They can't because they don't know how the customer will use the boat. They just go for a system specification likely to be suitable for most boaters - typically 4 to 6 110Ah batteries.

So why can't a boat owner do the same? I.e. just fit (say) 4 batteries?

[Alan de Enfield]

1 hour ago, David Mack said:

So why can't a boat owner do the same? I.e. just fit (say) 4 batteries?

 

I take it you are not being serious !.

 

How many boatbuilders do an energy audit? They can't because they don't know how the customer will use the boat. They just go for a system specification likely to be suitable for most boaters - typically 4 to 6 110Ah batteries.

 

The OPs boat has 2 batteries !

 

It is good business  for the bulder to 'get it wrong' as they sell more batteries.

It is good for the boat owner to get it right as the batteries will last more than a few weeks.

 

Whilst the builder doesn't have any idea how the owner will use the boat, unless it is part of the build specification, the boat owner will know how they intend to use it.

 

The OP plans to move every 3 or 4 days and then cruise a maximum of 5 hours so will require an estimated 800Ah battery bank, so, thats that side of the equation, now how do they get 450Ah back into the battery (running the engine, Solar, generator ???????)

Edited June 20, 2021 by Alan de Enfield

[ditchcrawler]

How many boatbuilders really know much about living on boats. Prior to LEDs I visited Crick and one of the show boats had probably 16 halogen down lighters at about 2 amps a piece. Is an incinerating toilet the best thing for off grid living.

[nicknorman]

20 hours ago, kalees said:

Hi all,

 

I am looking to replace my leisure batteries as I  would like more capacity. I currently have 2 105ah and would like to know if there would be any advantage to using 3 smaller ah or 2 larger ah to reach around 400ah, 2 would be easier due to space available?

 

for info, my only charge source is a single 100 amp alternator for the starter, bow thruster and leisure batteries, not sure if this has any impact on the way to proceed.

 

Jeez it get's harder and harder to get a straight answer from this forum these days!

 

If you want 400Ah out of 2 batteries, they will be huge and very heavy, making it somewhere between very difficult and impossible to install (depending on access).

So I would suggest 3 batteries. The only consideration with the single 100A alternator and a large capacity bank is that it will take longer to recharge a larger bank at the same state of charge, and the alternator will be working harder for longer which may have some impact on its life. Of course if you have a larger battery bank but only use the same amount of energy as you previously did, that doesn't apply. But having more capacity generally seems to result in more energy used (human nature etc!) and with increased energy usage it will be important to make sure the engine runs long enough to fully recharge. If you don't already have some battery monitoring equipment I'd say it is essential fit some, to ensure the batteries are fully charged regularly. Failure to fully charge regularly will kill the new batteries quickly.

[nicknorman]

16 hours ago, kalees said:

Hi all,

 

The reason for the question is that I suspect that the batteries need to be replaced and I was looking at this as an opportunity to provide us with some extra capacity. In terms of usage, I have an amp meter on the boat which shows the fridge drawing about 4 amps and the Webasto, when in use, another 4 amps. At the moment, beyond the charging of phones .01 amp and the inverter when on stands idle at 1 amp we currently use very little other power.

 

Looking forward, we are looking to spend a lot more time on the boat and may introduce a TV 12 or 240 V to be decided and the occasional charging of a Chromebook which takes 4 amps and will likely be looking to moor up for 3-4 days at a time and envisage a typical cruising day to be about 5 hrs.

 

As mentioned, we currently only have aa single 100 amp alternator and no solar.

 

AMG deep cycle batteries have been suggested.

It's certainly true that 2x105Ah is much smaller than average for a modern leisure boat. And whilst you don't say what size the inverter is, 2 x 105Ah will struggle to be able to provide enough current to run a high power device from the inverter.

 

A lot of people on here like open wet celled leisue batteres. Personally I have always found them to be pretty bad, which is why I first went to Trojan T105s and now to Lithium. I have never tried AGM but good quality ones seem much better than cheap open wet celled leisure batteries. The only thing to bear in mind is that expensive lead acid batteries can be damaged from failing to fully charge, just as much as cheap ones can. But with expensive batteries you have damaged more expensive batteries!