Black & Decker Cordless Drill will not charge battery

Both of my 18v and 12V chargers stopped charging. The 18V one is for a B & D trimmer and the 12v one is for a B & D drill. They charged last time but the next time they did not work. Neither of the Red and Green lights no longer light up. This indicates that the chargers are faulty. (If only the battery was faulty, then one of the red/green lights on the charger should still have been lit). I confirmed that the batteries do accept some charge by independently test-charging them with this bench power supply: http://www.altronics.com.au/p/m8303-powertran-30v-3a-regulated-bench-top-power-supply/ However, I found that the 12V battery needs replacing since it only reaches 10V, no matter how long it is charged.
I fixed my charger, see here: http://www.fixya.com/support/t24147879-b_amp_d_firestorm_18_volt_charger_model

Either the charging adapter is faulty or the battery is worn out.

If the recharageable battery is more than 3 - 4 years old then the battery could be worn out.Rechargeable batteries have a finite number of charge and discharge cycles andwill lose their charge capacity over time, i.e. won't charge to 100% andgradually the charge reduces until the battery won't charge up at all. OR Thebattery shows a 100% charge but when the adapter is disconnected the batterydrops off to zero capacity in a very short time. If the battery drops to anunacceptable charge level then the battery needs to be replaced.