This video shows an experimental set up of a domestic capacity UPS for fridges and freezers. It uses a Giandel inverter charger rated at 1000w and 25A-55A with a 100Amp-Hour deep cycle hybrid battery. The freezer is small but old technology, so it isn’t particularly efficient drawing about 100 Watts or just under 10 Amps from the 12 Volt battery.
This set up automatically switches to battery power and inverter mode if the mains power disconnects, and then back to charger mode when mains power reconnects. This gives a back-up power supply sufficient for around 5-7 hours duty cycle – for me that’s enough to get home from work in time to start a generator and stop food spoiling in the event of a grid black out.
Cost of the inverter is under AUD$200 and the battery is around AUD$220.