Hi Stuart
I never owned a Sprite but the electric hook up point on a 1980's C.L. Eccles Topaz that was my first caravan consisted of the blue male end of the ehu socket bolted to the underside of the caravan so that it poked out toward the front off side. The battery was stored underneathe the front seat on the o/s, there was no battery box or dedicated outlet but the cable poked up through the floor and into the fused trip. I used a normal car battery charger plugged into an extension lead off the 240v socket to charge the battery.
There are one or two Sprites from the 1980s for sale on fleabay complete with photo's and I'm sure that one of the vendors would be able to help
CI Sprite Alpine SV - 1980s era 4 Berth Touring Caravan
Item number: 300316328780
If not try re posting your question under 'Technical' or 'Buyers Guide - Caravans'