audioguru said:
How do you know when they are fully charged and are having their life shortened by overcharge?
As long as you only charge them slowly it doesn't do any harm, in fact you can leave them on 'trickle' charge permanently! - problems mostly occur when fast charging, one solution is to monitor the temperature of the cells, they get far hotter once they are fully charged. This is why it's common to have temperature sensors inside laptop batteries!.