comments:
I would go with a 12v LiFePO4 battery. Something like this: https://www.amazon.com/dp/B0FK9Z1MF2?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_27 This battery takes 14.4v to charge. So you can just wire a barrel connector jack in parallel with the battery. When the charger is plugged in the battery will charge and the amplifier will run off the 14.4v charger. When the charger is unplugged the amp will run off the 12v battery. You can't really do this with a 24v LiFePo4 battery because the charge voltage is 29v which exceeds the max voltage of your amp. Are you using a TPA3xxx amp? Another popular option is to use a 18v/20v Li-Ion power tool battery with an adapter which would allow you to quickly swap batteries and charge them with your power tool battery charger.