Kinda sorta except the cells can produce a finite/known amount of chlorone due to an exact amount of coating on the SWG cell plates. (Poor water chemistry or cell abuse lowers this further) Any other electronic or piece of equipment just dies from use or corrosion without an expected death date. The cells we know are expected to produce FC for 10k hours for the name brands. It can more or less be calculated like a gas tank.
The cell will still turn on and do everything except produce FC, once 'empty'. If protected from the elements and lucky in avoiding power surges, a control unit on the other hand, could last 25 years while you depleted 5 or more cells.
Exactly that.
With an electrical continuity reading. The higher the salinity, the more metal is in the water (sodium), the better it conducts.