Hey all
I have just connected 2x 12v car batteries in parallel. When I use this parallel set up to power a device only one battery will go flat. As if there is a problem with the circuit between the 2 batteries.
I have tested all the wiring to the circuit and it seems fine. I have voltage from battery 1 all the way to the terminals of battery 2 and vice versa.

There is also 2 low voltage cut outs on the circuit for when the batteries are connected individually. I have disconnected both of these to simplify the circuit and the batteries still do not appear to equalise with slightly different voltages (Battery 1 = 13v, Battery 2 =12.8v).

To be honest I have not checked whether or not amperage is doubling yet. I am assuming that this would not be the case as 1 battery is flattening while the other stays charged and that the voltage is not equal on the all points of the circuit.

Any idea's? I can't think of anything

 

Ok. I've tried a few different things and I've found the problem is the gauge of the wiring.

If I substitute the smaller gauge wiring with jumper cables the circuit works perfectly.

I will rewire the circuit with similar gauge to that of the jumper cables and it should do the trick.