i've been researching batts. for a spell here and came across this little chart that you may(?) find handy.
there is tons of speculation on battery life. my thought is that a typical cr2016 will last 5-6+ years if you use a decent one.
it is my belief that if a mfg advertises 2 years, the watch can stay on the shelf for a long time and still hit the advertised mark.
alarms and the light play a factor in a huge way also....just sayin'.
it may also help you with shopping. if you are having a hard time making a choice between 2 watches and one takes a 1215 and the other takes a 4588...you might want that 10000 year battery (i tend to speak in hyperbole).
of coarse solar would make the point moot.
just me being that helpful guy that you all know and love.
here's a link:
Batteriesandbutter.com - Watch battery comparison chart