We have just been to our local caravan accessory shop and saw a new (to us anyway) piece of kit! It is a trickle charge solar panel which attaches to the caravan battery and keeps it topped up whilst not in use (size 12" x 6" x1" approx). It would be ideal for use whilst the caravan is in storage and no electricity available. It only needs to be placed in a window which allows daylight through. Has anyone on forum used one?