I have a Makita 12v cordless drill which has a Fast Charger (DC1290A) and 1220 Ni-Cad battery. Problem is that the battery only charges for 4 seconds and the charger shuts down. I need some input to decide if the problem is with the charger or the battery, or both.

Look inside where the Battery terminals connect.
THey are flat metal springs inside the drills Battery hole.
Make sure the are not compressed down causing them not to touch the battery terminals of the battery.

ALso check the Brushes on the drills motor they may need replacing...

Selvol

I have a 12v an 18v Dewalt I can charge them both from the same charger

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Makita makes two 12V Ni-Cad pod batteries: Battery 1222/2.0Ah (PN: 192598-2) and Battery 1220/1.3Ah (PN: 192681-5). Makita's universal charger (PN: DC1804) will charge any Ni-MH or Ni-Cad pod or stick battery from 7.2V to 18V.

before you dump those batteries, check the charger. If the battery when charged runs the tool but dies out quickly then you are probably right. If the battery never seems to be charged at all, then it may be the charger.

As long as the charger voltage and the battery voltage match (7 volts) there should be no problem. A fast charger just runs more current thru the battery (per unit time) than a not-so-fast charger. If you notice the battery getting really hot when it's charging (like too hot to touch), stop using it.

Maybe your battery is died, you can replace it on

http://www.drillbattery.com.au/buybattery.php/makita_1220_power+tool+battery.html

Makita generally does not provide a schematic for the charger wiring. The only parts that are usually replaceable are the cord and housings and possibly a fuse. If this is an older charger I would look for a "cold solder joint" I fixed quite a few for this and one component breaking loose. I dont know if Makitausa website can help or not. What volt is this charger, I have a couple in my garage that I can look at also

You will need he correct charger, the 24V will destry a very expensive battery.