One of my np-e3's for a Canon 1D Mark II is not accepting a charge. I tried several times to fully refresh the battery, but the process just continues for days on end and never works out. Does anyone know if there's a way to fix this? How about what might have caused it? Have others run into this as well?
How old is the battery?, how many times do you think you have re-charged it?
Thing is with batteries, you only need one cell in the pack to go down and it acts like a resistor, thus not letting electricity flow through.
There are a few places over here in the UK that rebuild batteries now. This is good because they test each cell and only replace the defective ones, thus it is cheaper.
There is a way to fully discharge a battery by using a resistor, however, you need to calculate the resistor size for the output voltage/amp hour of the battery.
Have you dropped the battery?, if so one of the internal connections could have come loose.
Has the battery suffered extreme cold or heat?
Sorry for the dis jointed reply, just throwing ideas in as they come to me