If you have a rechargeable battery that has been fully discharged and does not want to take a charge don't give up on it! it just needs some science love. Here are a few things that you can do to rejuvenate the battery and get that charger to charge it.

 

Equilibrium Method

This is just like jump starting, only with the battery disconnected. The idea is that you take your dead battery, say an emergency exit light battery and a working battery like your extra vehicle battery and connect + -> + and - -> - with jumper cables and wait. This will equalize the available energy between the two batteries.

Over Volt Method

This works best with Lead Acid batteries, but it requires a higher voltage charger than the battery is rated. Same method as above. This results in a rapid charge, so check it regularly. This method will descale the lead cores in the battery helping the plates react with the hydrochloric or sulfuric acid in the battery creating electricity.

Partial Charge to a Pack of Batteries

If you have a pack of connected batteries and they will not take a charge, pull half of them and apply the above methods to the batteries. Fully charge them then replace them into the pack. This will boost the dead cells using the Equilibrium Method.