Differing battery capacity in same bank ok?

[Sulaire]

Time to renew the house bank, but cannot get the lifelines i want due to shipping to where i am, crazy prices.

Found a good local source for Vetus agm, but of course the physical size of the ones i want are too big...soooo...

Is it acceptable to mix capacities of same brand and battery type (agm) in same house bank in parallel, ie 2x 170 Ah plus 1x 220ah?

[S/V Illusion]

They will have different internal resistance. Consequently, they will all perform at the lowest common denominator of the weakest one drawing down the others.

[john61ct]

So yes you can, but not ideal for overall longevity.

Best to replace whole bank same model and age / mfg date

[sailinglegend]

Originally Posted by S/V Illusion

They will have different internal resistance. Consequently, they will all perform at the lowest common denominator of the weakest one drawing down the others.

Originally Posted by john61ct

.....Best to replace whole bank same model and age / mfg date

I'm afraid I have to disagree with the above opinions.

This has always been the common belief and is what most battery manufacturers would recommend, but since the OP is looking for Lifelines let me refer you to battery guru Justin Godber at Lifeline Batteries. His comments can be found here, but this is a subscriber Forum so I add Justin's text below:

http://www.morganscloud.com/2011/10/...battery-sizes/

Batteries of different sizes in the same bank.

“It has previously been said that this is not a good idea; however, we have done some pretty extensive lab testing and we can find no differences in the batteries. Age is important but size is not. You can safely mix and match battery sizes in one bank.

Also, Sabre Yachts does this from the factory. This was one of the reasons we started testing this scenario. Sabre use a GPL-4DL and when they want to upgrade a battery bank they add a GPL-31T.”


If you can get access to the site then read the comments which all agree and give further explanations as to why this does work, eg:

...."Given identical chemistry in all modules (e.g. all are flooded lead – sulphuric acid), the voltage profiles will match and they should balance the charge/discharge currents appropriately among themselves. I’m glad Lifeline’s tests appear to confirm what should theoretically be true; it does open up some more design options."...

...."in the situation you postulate, the 200 Ah battery would discharge to 100Ah and the 100Ah to 50Ah, assuming that both batteries were the same age and health. Therefore each battery would be at 50% charge at the end of the test and all would be fine. The reason is that battery voltage is a function of percentage discharge regardless of overall capacity. Therefore, as each battery discharges, its voltage drops in unison with the other and each battery will continue to supply current (amps) in proportion to size as it relates to the overall bank size."

I'm just replacing my Lifeline with three 4Ds and a Red Flash starter AGM which are being shipped from UK to the Med for £260. Because they are AGMs and considered 'non-hazardous' the shipping costs are relatively low.

[Sulaire]

Hi sailing legend

Thats funny, 3x4D plus 1 red flash is the battery system i have and has worked flawlessly for 10years now. Just starting to show signs of not holding charge now all this from 7 years living on board. Very good products.

I would have the same again in an instant but costs to ship to the canaries are huge, may i ask where you got yours in the uk? Maybe they can provide a better quote.

Vetus AGM is the best i can find locally, but will reduce house bank from 630 Ah to 510Ah, which just feels wrong, but should still be ok i reality i think.

[john61ct]

If all your batteries are Lifeline and the same age, I'm sure that's fine.

Otherwise I stand by my statement.

[sailinglegend]

Originally Posted by john61ct

If all your batteries are Lifeline and the same age, I'm sure that's fine.

Otherwise I stand by my statement.

So you know better than Lifeline batteries!

That just about sums you up - and we still don’t know who you are are even if you have a boat - so why should anyone believe any of your 50 posts a day?

Please, please fill in the personal details on your profile. You have been asked many times to do this. I believe we should all have to before we can post.

[sailinglegend]

Originally Posted by Sulaire

Hi sailing legend

Thats funny, 3x4D plus 1 red flash is the battery system i have and has worked flawlessly for 10years now. Just starting to show signs of not holding charge now all this from 7 years living on board. Very good products.....

Try equalising them. My bank was 1050Ah and have lasted 14 years, but i don’t intend to liveaboard for another 14 years so I am about to fit more solar so have reduced the bank size.

Also do a Capacity Test, mine were down to 55% last year. When I EQed them two got up to 45C so I have ordered new ones, but I can still get three days at anchor before they go down to 12.1v with only 140W of solar.

Lifeline suggest do the reserve Capacity test from full, which should supply 25 amps for 390 minutes. Or you do the standard test that lasts 20 hours at 10.5 amps, but it’s hard to keep the current constant for that length of time.

[Sulaire]

Ill try equalisation, buut...

problem is I single hand ocean passages, and on way down here low voltage alarms were going off at night, that was only 4 days, Atlantic last time was 3 weeks, do not want to risk having to hand steer for long periods, even though i have a wind vane, for dead down wind it does struggle with cross swell, autopilot is a power hungry beast and i hate engines!

I enjoy the peace of ocean passages and don’t want to be worrying about batteries![emoji3] i will most likely go for a new set, just wish it was lifelines not vetus!

[senormechanico]

Same type in parallel as long as same resting voltage, OK.
Same type in series NO WAY !

[john61ct]

Originally Posted by sailinglegend

So you know better than Lifeline batteries

No, but there are great differences between battery types beyond size, obviously less so within one company's offerings.

No thanks to the rest, MYOB

[Scrimshaw4]

Just out of curiosity have you "Shook" your batteries. My Lifeline AGM's are 9 years old and are doing great. I shake them once a year. Yes you can shake AGM's just like lead acid batteries.

[Sulaire]

Never heard of shaking batteries, everyday is a school day!

Reckon they got a good shake in the cross swell on the way to lanzarote![emoji3]

They weigh 60kg each, so will need someone stronger than me[emoji3][emoji3][emoji3]❤️

Thanks for the ideas, i am open to anything that will save me pulling these brutes out the bilges!

[Terra Nova]

Originally Posted by sailinglegend

So you know better than Lifeline batteries!.t.

You are drawing conclusions far beyond what Lifeline's representative has actually said (regarding their own batteries).

[john61ct]

Exactly my point