Ralph Posted September 18, 2007 Share Posted September 18, 2007 I have a 110AH battery on my MH but for the sake of convenience I bought an 85AH as a backup. I keep the spare in a small external locker and only swap over to it when the main battery goes down, which is not often :-S (I wonder why ther's no smiley for crossed fingers...) However to charge the spare I usually cart it into the garage and use a car battery charger and the van's charger would, I expect be much better (voltage, current etc.) So can I just connect the second battery in parallell with the main when it's on charge on the driveway? I would expect both batteries to settle and be OK but have I missed anything? Link to comment Share on other sites More sharing options...
michele Posted September 18, 2007 Share Posted September 18, 2007 Ralph, There is an old saying IF you don't use it you loose it. Running it parallell would be the better option seems an awful waste leaving it not used at all and only charging now and again.. lets see what the others think... Link to comment Share on other sites More sharing options...
crinklystarfish Posted September 18, 2007 Share Posted September 18, 2007 Hi Ralph.Always better to match batteries wired in parallel with ones of equal age, condition, and ideally capacity.You’re unlikely to get the best out either if you wire the two you mention in parallel. Better to charge them independently. The little one you use as a spare will discharge of its own accord while waiting to be used, so really, the best solution, if you want to up your capacity, is to get a couple of matching new ones and permanently wire both into the leisure side. Link to comment Share on other sites More sharing options...
michele Posted September 18, 2007 Share Posted September 18, 2007 Thats what I was saying it just takes me longer :D Link to comment Share on other sites More sharing options...
Clive Posted September 18, 2007 Share Posted September 18, 2007 Steve is correct regarding the preferance of having similar batteries for paralleling, but I don,t totally go along with his conclusion. If the second battery is the same technology as the first(wet cell, gell cell, AGM etc. being different technologies) and of similar age then it would be better to connect it directly in parallel with the first leisure battery with fat cables and suitable fuses. This way both batteries would share the load and the charging. The individual distarge rate of the batteries would be less so their effective capacity and life would be increased. C. Link to comment Share on other sites More sharing options...
Ralph Posted September 18, 2007 Author Share Posted September 18, 2007 I probably didn't explain myself very well. (Ah! no change there then...) I understand that unmatched batteries aren't a good idea but I'm only talking about connecting them in parallell at home to recharge, not to actually use them parallell. I don't really have the room to fit a second large battery. The 85AH is a lot lighter and smaller than a 110 and I only use it occasionally but of course I need to keep it charged, hence the idea that I would just connect it up occasionally to recharge. Not particularly easy to permantly connect them either as they are some distance apart. Link to comment Share on other sites More sharing options...
Clive Posted September 18, 2007 Share Posted September 18, 2007 Are you not able to run the cables through the floor, under the vehicle and pop them up again in the other enclosure? Link to comment Share on other sites More sharing options...
Ralph Posted September 19, 2007 Author Share Posted September 19, 2007 To be honest Clive I had assumed, until reading your post, that connecting 2 different capacity batteries would be no use anyway. But they are both of the same type and approximate age. If I did as you suggest what size cable would I need to use? The run would be about 3 metres altogether I expect, and how would you suggest I fuse it (ie: what type and size?) I really don't know what sort of current I should be sizing for. Thanks for the help. Link to comment Share on other sites More sharing options...
Clive Posted September 19, 2007 Share Posted September 19, 2007 Hello Ralph, OK, for about a 3 metre run you will be OK using 6mm sq cable. I would fit a 15 amp fuse each end, one near the original leisure battery and another near the new battery as both batteries are sources of power should the cable get trapped mid way somehow. If you have a good chassis connection near the new battery then the negative need only be connected to the chassis with 6mm sq cable. My suggestion would be to use Automotive type BLADE fuses and holders which can be obtained from Halfords and many other auto outlets. Don,t forget, when you do this work disconnect the NEGATIVE lead from the leisure battery first. When you complete the work connect the NEGATIVE leads to the batteries last. Hope that helps. Link to comment Share on other sites More sharing options...
Ralph Posted September 19, 2007 Author Share Posted September 19, 2007 Clive - 2007-09-19 2:10 PM Hope that helps. Very much Clive, thanks a lot :-D :-D :-D Link to comment Share on other sites More sharing options...
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