i got blackspor 20.4 cordless drill when i place the bettery to on the charger red light appear and slowley disappear

kash, January 2013

Most of the time, when those batteries don't charge, it's due to a dead battery, not a charger fault.

Todays rechargeable batteries are Li-ion.
Li-ion batteries are killed by been left drained to long.
They slowly loose charge when not used and need a maintenance recharge about every 6 months of storage as a precaution.

Electro, August 2013