Steve avatar image
Steve asked

What is the correct connection for connecting parallel batteries to system?

This may be stupid question buy how should three parallel batteries be connected to the system? I had an old-timer RV'er tell me that the positive should go to first battery and the negative go to the last battery, as per the photo I've attached. Is this correct, or does it matter?

battery charging
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1 Answer
Justin Cook avatar image
Justin Cook answered ·

@steve, I always prefer to see paralleled batteries all connected to a POS and NEG busbar with cables of as-close-to-identical length as possible, with the loads and chargers then connected to those busbars. This ensures that charge is applied -and load is drawn- equally from all batteries. That being said, the technique pictured above (POS to first, NEG to last) is my second preference; this connection technique also ensures that current flows in and out of the batteries in as balanced a way possible.

The parallel connection method to really avoid is having both your POS and NEG cables attached to a single battery, with the additional batteries jumpered off the first. I see this done remarkably often, and although it technically works, of course, it also guarantees that none of the batteries will ever be at the same SOC, and also guarantees failure of the first battery sooner than the others because the first is the one being subjected to the most cycling.

Bottom line: what you have pictured above is appropriate.

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Steve avatar image Steve commented ·

Thanks Justin, when I first purchase the RV the load/charge cables were attached to the same battery with 4 AWG cables connecting each battery. I had horrible storage problems and ended up replacing the original batteries 3 weeks after I purchased the RV, and I upgraded to 2 AWG jumpers. I'm seriously considering buss bar, would have earlier but the battery studs created a reason to not do it at the time of battery purchase.

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Justin Cook avatar image Justin Cook ♦ Steve commented ·

Yes, in a lot of RV applications with limited space we find that the preferred busbar method isn't practical because of the additional space required as well as the additional cabling... with a slide-out tray like this (if you can't mount the busbars to the tray) it can be a real hassle to be pulling out a tray with six cables coming off of it rather than just two... but if you can reasonably mount busbars and make your connections that way, it really is a far better solution.

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