My next door neighbour is upgrading his power cables to 19mm dia, 300Amp lines. He has lead acid 1000Amp hours. Lead acid needs gentle use. So never take them below 80% fully charge. That is only 200Amp hours of power you have. So you can only remove 200 amps for one hour and your done. So the need for 300 amp wire is overkill and a waste of money.