Compressor fridge at +4Deg C will run for 5 days from a cheap 120Ah LA battery.
To get a 120Ah LA battery from 50% capacity back to 100% takes 23 hours with one of the chargers that fleck2 describes.
To ensure you don't run your LA battery to below 50% capacity, keep an eye on the voltage, plenty of charts on google, you just need a pocket multimeter to check the voltage.
Better still, get a battery monitor, I use the Aili Capacity tester TR16, got one from China recently just £28 but will help keep my battery in tip top condition, and prevents me from running it to below 50% capacity.
Brilliant thank you everyone!
Actually, if I got a lithium battery and a deccompressor fridge...... wouldn't need a solar panel.....is that correct...I know these batteries are pricey.....but it seems easier in the longer term?
To keep things sensible price wise, you are better of getting a cheap 120Ah LA battery, for around £90 that will keep a compressor fridge going for 5 days without damaging the battery, as it will be down to about 50% capacity, then a cheap Aldi charger will get it back to 100% in around 23 hours.
In fact if you add in a 100 watt solar panel and MPPT controller, so say another £120 that would keep the battery going almost indefinitely. so there's £210 add another £290 for the compressor fridge, and that your budget £500.
You can alway get a LiFePo4 100Ah battery when they come cheaper in a few years time, by then your 120Ah LA battery will be about ready for replacement in any case.