I wouldn't recommend keeping a battery on the charger once it's fully charged. This actually reduces it's average life-span. This goes for cell phones, laptops, pad devices, etc. as well as the PV batteries.
To give an example, my wife and I both got our smart phones at the exact same time. She charges her battery and then is on the go all the time, only plugging her phone into the charger when it drops to 1 bar left. I on the other hand am running around in a vehicle most of the day and have mine plugged into the charger most of the time and have it plugged in at home every night. (Part of my OCD nature just likes to see those full bars dangit!). In summary, after 1 year, HER phone still lasts 3 days or more on a single charge, (depending on use), while mine is lucky to go 1 full day without needing a charge. I've noticed the same trend with laptops. Keeping it plugged into a charger without letting the battery run down in between seems to make them last less time between said charging.
Did any of that make sense?...
Anyways, I make sure my batteries are charged, but once that green light flashes...it's off the charger they come (except maybe the pass-through
), I want their charge life to remain as long as possible....for as long as possible.
* and my 650mah pass-through will last about 14 hours between chargings (though I usually have it tethered when at home)...my 1000mah lasted 2.5 days when I tested the full life on it.