I might ad, there are two different kind of battery's.
The car battery, which is unhappy if you make it empty. After being empty it will only have 80% of its capacity left. After a few of these events the battery is gone.
I use a traction battery, (gel battery) what they also use in electric forklift.
It gives a steady supply of energy and doesn't mind if you drive it empty.
I have a 105 amp traction battery so I can drive about 60 miles.
For my second C5 I will buy a 80 Amp traction battery because I find the 105 Amp version a little bit to big and heavy. I hit it with my heel if I pedal.
As far as I know they use the traction battery also in caravans, for the light etc. You need a special loader for it. Mine costed iincluding the loader 140 GBP.
greetings
Frank