If it is nicad you should'nt charge it till its almost dead also they constantly need attention when to charge and how long to charge.

The new batteries, lithium ion or lithium polymer uses embeded devices that reads the battery temperature and charge current wave that is also timed so you can let it charge all night. If it is left on all night it charge for an hour or so them stops and goes into sleep mode. Since this new batteries do not have the memory effect so you can charge them whenever you want.

New cellphone are pretty smart, Im sure yours too.