[singingboyo]

I usually charge my watch while sleeping and grab it in the morning along with my phone, but I'd assume a second watch would work? It's an expensive route with the watch, but it's a solution in many other spaces. My wireless headset, for example, has a replaceable, rechargeable battery.

For best results, you'd want to use a single charger, and to always put the alternate on immediately.

That said, the watch can notify when charged, which might be a better first step. The settings for that live in the sleep settings, of all places, but might be worth a shot?