Split Charge / Battery Age Etc Etc. (1 Viewer)

CandC

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I have just started the upgrade of the 12v system on our renault trafic autosleeper and thought I had pretty much everything covered through lots of research. I say, "thought" as something got me thinking about it again and decided to ask some advice :)

I'm going to be doing a total rework of the battery side of things, installing a solar panel and a two way voltage sensing split charge relay to keep everything topped up, whether from alternator or solar.

I know that it's been said many times before that a pair of leisure batteries should be of the same type and age in order to let them both fully charge and I understand the reasoning behind this. I've bought two new leisure batteries from go outdoors... 75AH and 110AH. The thing is, I didn't buy a new starter battery at the same time. Am I correct in thinking that once the split charge relay opens I will effectively have a bank of three batteries comprising the two leisure and one starter battery? If so, does that mean that I should buy a new starter battery too? The one currently fitted is of unknown age, but still showing strong charge on an LED type battery / alternator voltage tester.

Opinions please... the relay, cable etc etc arrive tomorrow (y)

I'll do a full write-up on the electrical makeover as I go along in a seperate thread but for now, thanks for taking the time to read this :D :hi:
 

Wildman

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well the new leisure batteries are not a pair as they are different capacities and that will probably result in a problem. However other people have mixed different battery sizes. Do note the voltage shown does not represent the charge. The leisure batteries in my van are on their way out, they are a pair of 110 amp/hr batteries purchased in 2001, they hold a charge that does not drop below 12.9v. however the current they are capable of producing has fallen so that once the sun goes in we only have 8amp (2 x 4amp/hrs) of useable power before the controller shuts down because of low voltage. If unused the voltage holds up all night no problem, so voltage off load is not an indication of capacity.
 

pappajohn

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well the new leisure batteries are not a pair as they are different capacities and that will probably result in a problem.
That will never be a problem.
The charger, no matter what kind, can only see one large battery so cannot overcharge the smaller one or undercharge the larger one.
It will charge to full joint capacity of 185ah.
 

ES Cumbrian

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As wildmans says voltage isn't everything and a solar panel can hide a failing battery. You should be OK with the two new leisure batteries as they are going to be well looked after by your system. Personally I would not buy a new engine battery until it starts having difficulty turning the engine over.
 
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CandC

CandC

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Thank you for the replies so far ;)

I would love to have two 110AH leisure batteries, but due to space constraints, that just isn't possible. I've read a few threads debating whether capacities in a battery bank need to be matched or not. It would seem to me that using large enough amperage cable (sorry if I get some of the lingo a bit mixed up, but I'm sure you get the gist...) would make the voltage drop in the joining cables negligible and, percentage wise, the drain on the capacity of each battery would be to all intents and purposes the same.

Thank you for explaining how voltage isn't necessarily an indicator of battery condition, rather it is the capacity which deteriorates. Did I get that right this time? :)

My main concern is that if the starter battery has deteriorated, would that have the same effect as putting a brand new leisure battery in a bank alongside a worn out one whereby (If I have understood correctly) the new battery will only charge up to the maximum capacity of the old?

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ES Cumbrian

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Your batteries will all charge up to full "voltage" as determined by the alternator or solar regulator. Each one will charge up to its own "capacity" the only problem would be if one of the batteries had a serious problem like a shorted out cell but yours seem fine.
 
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CandC

CandC

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Your batteries will all charge up to full "voltage" as determined by the alternator or solar regulator. Each one will charge up to its own "capacity" the only problem would be if one of the batteries had a serious problem like a shorted out cell but yours seem fine.

That's great, thank you. I'm still not sure if I used all the right words or not ;) but people obviously understood me. Thanks again to all for replying and especially for doing it in easy to understand chunks! (y)
 

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