High Power Battery System: Variable Input DC Voltage to Fixed AC Output Voltage
Actually you do not need a DC-DC converter. I assume you are thinking of buying an inverter of the shelf, something like this,
https://www.banggood.com/Intelligent-Color-Screen-Pure-Sine-Wave-Power-Inverter-12V24V-To-220V-3000W4000W5000W-Converter-p-1243542.html?rmmds=search&amp;ID=534726&amp;cur_warehouse=CN

These inverters are supposed to go with lead-acid batteries either 12 V or 24 V, so it does not need the exact 12 V or 24 V it supports low voltage up to 10 V or 20 V as the battery voltage reduces when it discharges.