imported post
Light as power source
Most Eco-Drive watches are equipped with a special titanium lithium-ion secondary battery that is charged by an amorphous silicon solar cell located behind the dial.[2] The titanium lithium-ion composition precludes it from being affected from the regular charge/discharge cycle of other types of rechargeable batteries. Light passes through the covering crystal and dial before it reaches the solar cell.[3]
Depending on the electronic movement model, a fully-charged secondary power cell could run with no further charging anywhere from 30 days to 3,175 days (8.7 years).[4] If kept in the dark for too long, some movement models engage a hibernate mode, where the hands of the watch would stop running but the internal quartz movement would still keep track of time. If an ample supply of light is given, the hands would move to the proper positions and resume regular timekeeping.[2]
from -
http://en.wikipedia.org/wiki/Eco-Drive
