Avia used various electric and electronic movements in their watches but those in the first section below are very unusual.
The following photographs are kindly provided by David Read, who owns these very rare Avias. Unlike the many other watches that employ the Landeron 4750 electric movement, these Avias have a rechargeable accumulator rather than the more usual disposable battery. More information from David:
Avia were the first watch manufacturer (or assembler if you prefer) to put the Landeron Ebauche on the market and they chose to use the rechargeable battery version because it allowed a slimmer case. It was also the first electric watch in the world to to use a rechargeable accumulator since the earlier Lips, Elgins, Epperleins, Hamiltons etc, all used cells with non-reversible chemistry.
The UK Avia announcement was made by their agent Lous Newmark in December 1960 and for the initial production the movements were put in very substantial cases of 18kt rose gold with black and gold dials. It made for an extremely handsome watch as you can see. Because of the chance of losing the setting crown that serves as a cover for the charging socket, these watches were issued with two.
I subsequently found two later examples in gold plated cases. I have restored all three watches and the 4750 proves to be an excellent timekeeper; better than most other electrics in my experience. As for the Accumulators, the one in the gold case still has some chargeable capacity, lasting about three weeks. I wear the watch every so often, simply putting it on the charging adapter the night before as shown in my image.
My photographs illustrate both the recharging adapter and a detail of how the 80 mA Leclanché cell is held inside the case back with a screwed ring. At first this ring was was made in hardened rubber or Ebonite whilst the later ones used transparent nylon. You will notice a curiosity. When the very first Avia electric watches in gold were made, (very few I imagine), they seem to have made the mistake of printing Electronic on the dial. This was corrected for those that followed and these either have Electric on the dial or nothing except an electric symbol at 12.
These Avia Swissonics are pretty easy to find and must have been a good seller when they appeared in the early 1970s. They all contain one of the ESA Dynotron movements.