I have two 160ah lesure batteries and LED lights plus a fridge (Waeco CR40 compressor) and various 12v charging things.
With the fridge on I can easily run for about 4 days, without the fridge..ages. Current plan is to add a 100w ish solar panel on the roof which xshould help eek that out a bit. Will cost about £400 fitted from http://www.travelvolts.co.uk
What is the invertor for? Laptop or ipad? If so you are inverting 12v to 240 to then be inbverted back by the PSU, so maybe look for a 12v charger or usb charger..
Old Play stations are 12v, as are many little LCD tvs…if you keep everyhing DC life will be simpler…