Wire Size For Connecting Two Leisure Batteries Together.


New Member
Apr 28, 2020
Hello all.

Thank you to all for welcoming me to the site in my recent introduction thread and encouraging me to ask questions.

I would be grateful if anyone can help me with wire sizes. How do I best determine the wire size to use to connect two 110AH, 12V batteries together?

The system is / will be:

1. 250W solar panel (this will increase to 2x 250W panels for a total of 500W).
2. 40 amp solar charge controller.
3. I haven't bought my inverter yet, but lets just say 2000W so that I can have anything up to that. I'm sure I will not want anything bigger.
4. A Stirling battery to battery charger (likely to be 30 or 40 amp models). I haven't bought this yet either.
5. Two 110ah 12V batteries.

I understand that length of wire is is a factor, but this will be minimal as the batteries will be placed next to each other.

At the moment I have taken 2000W / 12V = 166.67A. I feel that 25mm² rated at 170 amps is too close for this and so I am thinking about using 35mm² rated at 240A wire.

I have read that bigger is better with regard to joining batteries. Do we think 35mm² is big enough, or do people go bigger?

I welcome any and all input in this.




Active Member
Apr 22, 2018
Peak District, Derbyshire
I have 2 x130 amp leisure batteries connected with 35 amp rated wire and 2000w inverter connected with 25 amp. This is more than adequate. Remember when taking power from leisure batteries to connect +ve's from one battery and -ve's from other battery. This equals out the loads when discharging or charging. hope this helps Dave.