This is the last iteration of the battery. Using spot welding and some creative work, the battery pack is done. Picture attached. This is a 1 Ah battery, 30mm x 6mm , which at 10uAh including self-discharge will last about 10 years (10% self-discharge). The battery is non-rechargeable. Future iteration will add a rechargeable battery with solar harvester which will bump up the life indefinitely as the watch needs to be recharged only once every few years and the typical deep-discharge-charge cycle is about 100 times.

I still need to solve the problem of battery connector and housing, as currently the battery is relying on hand-made kapton tape insulation and hot-solder leads.