adding one more Lithium, wiring thoughts?

[PS Cruisign]

Hi all,

Im going to add another 100amp lithium to my bank for a total of 300. On my Four Winds Super C, two batts go under the steps. I am going to put the third one in this area next to the entrance steps. It houses the inverter and my solar install(and plenty of dust from desert camping)! Question is connecting it to my bank which is monitored by a Victron 702.

Obviously I can run wires underneath the coach however, but that would be a four foot or so run which brings sizing into play and manipulating wires. I was thinking outside the box. Could I just tie into the 2/0 that comes out of the batt bank which is fused and runs to the inverter? (see pic) The wire coming into the fuse is always hot 13.2V. Then use the inverter chassis ground for the negative, because the inverter ground is tied to the battery bank so I can monitor amp draw from the inverter. If this would work, it would keep the runs under two feet so I could use more flexible 4/0. My thinking was it is just a big loop and as long as positive to positive, that would make it parallel still and the solar could get to the additional batt.

Thoughts?

[Chateau_Nomad]

The important thing is to make sure all cables connecting all the batteries in parallel are the same gauge AND same length... otherwise you will create a charge imbalance between cells.

Not sure I understood if you're adding the third battery close to the other two?? But you definitely don't want an "orphan" battery a distance away from the other two... with a much longer cable run than exists between the original two batteries.