Here's the data sheet on the Battery:
http://www.cavediver.com/batteries/Np18-12.htm
As you can see, here's the discharge percentages for an unconnected battery:
1 month = 97%
2 months = 91%
6 months = 85%
So as you can see, it is not fast, but it IS significant if you don't float charge them for a year or so...
Also, look at the Life Expectancy numbers:
If you
totally discharge them (like many teams do) you'll only get
180 cycles out of them, but you if you only discharge them 30%, you get
1200 cycles!!! That's over 650% better life expectancy!
Therefore, the "shallower" you discharge them, the better their life expectancy. In fact, you can even float charge them
forever with the smart charger and it won't hurt them.
That is why I recommend:
1)
Never running a battery dead,
2)
Always leave one float charging (your charger should be
kept busy),
3) Rotate
all team batteries at least monthly onto the charger to keep them topped off,
4)
Immediately recharge
any battery used for even simple robot tests, and
5) During heavy testing, if you
have lots of batteries, rotate through your batteries frequently even within one day (esp. between major tests) so no one battery is pulled down very far, then recharge them all immediately.
- Keith