Hello Ian,
If it is only for battery charging then the smaller unit will be fine. and will probably cover the TV as well. If it is for other applications such as heating then use the gas alternatives, which are much more fuel efficient,Quieter and the fuel is cheaper too.
Just please be aware that despite the name that says silent, - they are not. They do make noise and some people find it very annoying.
There are times when only a generator is the answer, but I find that with careful power usage certainly a long weekend is possible. (drink a G&T instead of watching Eastenders, or go to bed earlier!)
There are alternatives - depending on your length of stay, and the power usage the batteries with a greater capacity e.g. 110AH) may last the duration of your stay. You might consider a second battery that is charged in your car whilst travelling around, and swapping to the caravan it when necessary.
Choose sites with Hook Ups. or a 50W solar panel will top up a battery and cover a substantial proportion of a caravans daily power needs.