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Tesla · 04-06-2012, 04:57 AM

I mentioned the issue of parallel connections, read that many years ago and there are numerous issues as even "equal" batteries are never truly equal.
Below is a quote from a thread I just looked up, someone elses explanation of one of the problems:

"mrebmen,
you can hook Pb in parallel, but you should be aware of some limitations.

In the RV arena, none of the coach makers put PB in parallel any more. They found out after years of testing that while charging in parallel is fine, in discharging one battery gives its "all" first and the other "loafs". The two batteries have different internal impedences, so one battery is always being discharged more than the other. As the battery ages, the lower impedence battery is always giving max current and therefore its PB plates are undergoing sulpharization more rapidly than the other. So one battery dies of "old age" while the other has only given half of its life cycle. And the problem is that the dying battery now starts to pull down the "loafing" battery. In short, the two batteries do not yield anything like twice the lifetime of a single battery. That is why the RV coach batteries have two marine 6 volt cells in series rather than cheaper 12 volt deep discharge in parallel. You get longer battery life with the two in series.

Some people have negated this problem with the following. They put knife switches on both batteries in parallel. They always charge in parallel. When its time to use the coach battery, they shut off one switch. When that battery starts to get low, they reverse the switches and keep going. This tends to give equal use to both batteries and gives a longer service life. The only problem is remembering to set the switches.

Hope this helps.
Crazy Ted -- a battery junkie "

Link:Can I hook up Lead Acid batteries in Parallel? - RC Groups

Every traction battery, remote power supply, house supply I have ever seen has been individual 2V cells connected in series, if more power is required they use a larger 2V cell, or alternate between 2 banks of batteries.
Good luck with it.

04-06-2012, 04:57 AM	#3 (permalink)
Tesla Master EcoModder Join Date: Feb 2012 Location: Australia Posts: 355 The Truck - '02 Nissan GU Patrol ST Thanks: 5 Thanked 76 Times in 50 Posts	I mentioned the issue of parallel connections, read that many years ago and there are numerous issues as even "equal" batteries are never truly equal. Below is a quote from a thread I just looked up, someone elses explanation of one of the problems: "mrebmen, you can hook Pb in parallel, but you should be aware of some limitations. In the RV arena, none of the coach makers put PB in parallel any more. They found out after years of testing that while charging in parallel is fine, in discharging one battery gives its "all" first and the other "loafs". The two batteries have different internal impedences, so one battery is always being discharged more than the other. As the battery ages, the lower impedence battery is always giving max current and therefore its PB plates are undergoing sulpharization more rapidly than the other. So one battery dies of "old age" while the other has only given half of its life cycle. And the problem is that the dying battery now starts to pull down the "loafing" battery. In short, the two batteries do not yield anything like twice the lifetime of a single battery. That is why the RV coach batteries have two marine 6 volt cells in series rather than cheaper 12 volt deep discharge in parallel. You get longer battery life with the two in series. Some people have negated this problem with the following. They put knife switches on both batteries in parallel. They always charge in parallel. When its time to use the coach battery, they shut off one switch. When that battery starts to get low, they reverse the switches and keep going. This tends to give equal use to both batteries and gives a longer service life. The only problem is remembering to set the switches. Hope this helps. Crazy Ted -- a battery junkie " Link:Can I hook up Lead Acid batteries in Parallel? - RC Groups Every traction battery, remote power supply, house supply I have ever seen has been individual 2V cells connected in series, if more power is required they use a larger 2V cell, or alternate between 2 banks of batteries. Good luck with it.