Battery Bank Wire Size

1L243 wrote:
I built my battery bank four 12 volt deep cycle batteries with 340 amp hours.

Any thoughts.

Assuming you are using 4 FLA "group 27" RV/marine batteries which would be about 79-80 Ahrs each.

The voltage sag you are seeing with that kind of amperage and time is normal with those batteries and should be expected and should be well within the operating parameter of the inverter without shut down.

RV/marine batteries are a hybrid deep discharge/staring battery and as such they do neither function well. They do not do deep discharge well nor do they work all that great as a starting battery.

The battery voltage should and will "bounce back" some once the heavy load is removed and that is normal and to be expected.

You are asking a lot for the small amount of capacity and the type of batteries you have. Your dealing with smaller, thinner plates in RV/marine batteries. Thinner plates in theory should give you a high amperage draw in a very short burst like for a starter, but for your specific use it is far longer than what a starter runs and they will fall flat on you.

For greater capacity in FLA, 6V GC2 batteries would be a better choice but with loads over 100A for 2-5 minutes at a clip, 2 pairs may be needed.

Alternately one pair of 6V GC2 batteries in AGM form due to lower internal resistance loss might actually work better for what you want. Although the AGM versions typically cost $10-$20 each more and will have a few less Ahr capacity. I don't typically push AGM, they do have a few shortcomings and habits I don't like, but one big plus for them is the voltage drop under high amperage loads will be a bit less than FLA.

I don't think the issue is your interconnects but rather the battery choice.. Much better batteries out there than RV/Marine combo batteries.