# Dual 12 V battery setup - wiring, grounding and busbars

I am installing a second 12 V battery into my van to run eletronic devices. The second battery is a bank of two LiFePO4 12 V, 120 Ah cells connected in parallel.

My three questions are surrounding the circuit diagram pictured below:

1. Is running a ground from the negative pole of Lithium 2 to the negative pole of the starter battery sufficient to earth the system?
2. Is the green Inverter ground wire earthed if I connect to the negative BusBar (going to negative of battery bank), and what should the rating of the negative BusBar be?
3. What should the amp rating of the positive BusBar be?

I understand cable needs to thick enough to carry the amps in that circuit, e.g. the circuit with fuse block needs to include wire rated for 100A. What about the interconnecting batteries? Should this be rated for the largest circuit, i.e. the 550A from one of the positive BusBars?.

• In vehicle minus is usually a vehicle chassis. Commented Mar 23, 2021 at 12:45
• You're planning on connecting two chargers to the same batteries? Commented Mar 23, 2021 at 12:49
• Why two +ve bus bars? It would be simpler to have 1. The current rating? Sufficient so that they can handle the maximum current without getting too hot. Remember - the fuse protects the wire, not the load. The bus bars should be the point of distribution, so the -ve wire to the existing battery should connect to the -ve bus bar. You probably want fuses on each of the batteries to protect the wire. Commented Mar 23, 2021 at 14:04
• @Finbarr - yes, one charges from PV, one from the alternator of the vehicle. Just incase we stay parked for a while, or the sun isn't shining. Commented Mar 24, 2021 at 0:39
• @Kartman - Two +ve bus bars mainly because if they were on the one, the current rating would be around 640A and I wouldn't know where to source a bus bar that can handle such ratings (in Australia). Will fuse between the +ve bus bar/s and the battery (however many there ends up being). Noted re: -ve bus bar. Will connect a wire from -ve of car battery to -ve busbar (rather than -ve of lithium 2), then -ve bus bar to lithium 2 -ve. Hope this is correct and thank you for your reply. Commented Mar 24, 2021 at 0:45