We are upgrading our battery bank, but rather than just not using the existing ‘old’ batteries at all there would be an issue with keeping the existing batteries as a sort of "spare" battery bank - basically having a switch between the two battery banks- and if the new battery bank was getting too low we could manually switch to the other bank and utilise that- switching between them also to charge.
I don’t yet know the exact specifics of the new battery bank but we are looking to have at least 300Ah total.