Hooking up two 12V batteries

[aufinger]

I was checking my batteries today and I noticed that it's not setup exactly the way it's shown on the sticker inside my battery box. The sticker shows the unit's positive lead to the positive side on battery 1, and the unit's negative lead to the negative side on battery 2. However, when my dealer installed my batteries, they connected both unit leads to a single battery. I'm not having any battery problems, I'm just curious if it makes any difference where the unit leads are connected.

[dangerranger]

Take a pic of how they are connected. If done improperly it may still give 12v, but not a balanced discharge. [ one battery doing more work.] DR

[Rhumblefish]

I've seen parallel battery wiring done both ways (like the middle illustration, as well as the OP's likely setup, with + and - leads going to ONE Battery, and then both terminals connected to like terminals on a SECOND battery), but I prefer the version in the illustration. It makes me think the battery bank is "working better" and that all the cells are properly engaged, but I am a moron about these things.

Just my .02 (which is likely not even worth that much).

[Thomas ho]

you can buy a Minkota brand ALTERNATOR CHARGER. I HAVE it in my boat ,and jt will work in a r.v. wires go to + and - ,then the other leads go to the 2nd battery. they come in 1 battery, 2 battery, etc.

[Bob K4TAX]

It is OK the way the dealer connected the batteries. BUT.... a better distribution of current occurs when they are connected in the manner shown in the 2nd picture "Hooking up 2 12volt batteries".

Bob

[aufinger]

Thanks for the input. I think I'll change it to the way shown on the sticker.

[Chuck_S]

The diagram in your trailer is correct and helps equalize discharge and charging otherwise the battery both cables are connected to gets first charge and first discharge. Earthshakingly important? Nope but the best solution is still the best solution.

-- Chuck

[pgandw]

Please, please put a fuse (50A?) in one of the paralleling wires. This prevents batteries from going up in flames (literally) if something goes wrong in one of the batteries. Been there, done that, have the singed t-shirt.

Boiling battery acid because 2 mismatched batteries are connected creates the prettiest blue flames I have ever seen coming out of the battery vents. And the melting parallel wires glow a pretty red with insulation drips to add to the picture.

If a cell in one of the batteries shorts out internally (fallen lead at the bottom of the cell), a 2 volt imbalance occurs which drives a hundred amps through those parallel wires for as long as the good battery lasts (it overheated and boiled its acid too providing that kind of amperage).

I put out the fire and ended all the boiling acid in seconds by cutting one of the parallel cables with lineman's pliers. Meanwhile, the battery with the short had blown holes in the case top.

You don't have to be me. Put a fuse in the parallel wires. Or go to GC-2 6V batteries in series like I did.

Fred W
2019 Flagstaff T21TBHW A-frame
2022 Hyundai Palisade

[aufinger]

Originally Posted by pgandw

Please, please put a fuse (50A?) in one of the paralleling wires. This prevents batteries from going up in flames (literally) if something goes wrong in one of the batteries. Been there, done that, .....

Fred W
2019 Flagstaff T21TBHW A-frame
2022 Hyundai Palisade

I recall that my first camper, a single battery Coleman pop-up had a 30A in-line fuse on the battery. None of my subsequent campers did.

[pgandw]

Originally Posted by aufinger

I recall that my first camper, a single battery Coleman pop-up had a 30A in-line fuse on the battery. None of my subsequent campers did.

The extra fuse is only needed when batteries are put in parallel, and must be in the paralleling wires. If there is any difference in voltage between batteries in parallel, a current proportional to the voltage difference WILL flow. Due to the low internal resistance of a battery, this current can be substantial. One cell shorted out means a nominal 2.1 volt difference between the batteries in lead acid batteries. In LiFePO batteries, cell voltages are around 3.4 volts, with a lower internal resistance of the battery.

The fuse in the paralleling wires prevents the imbalance current from getting to the fire starting point.

Fred W

[ppine]

Door number 2.