I have a 12v dewalt drill driver DW907K-2 haven't used for a while. Charger doesn't seem to be working - light just flashes, from what i can remember this isn't charging.....or does it flash until its charged ????

Some battery can not be charged by fast charger, because this can damage the battery. You can think to replace it to a new charger, a 7.2V 9.6V 12V 14.4V 18V NI-CD NI-MH BATTERY charger for Dewalt

Bad Battery pack, check voltage, try jumping nickel/cadmium battery with car charger, then put on charger.

Here is the manual for the charger - note on page 2 the meaning of the problem you describe - time to replace batteries (depends how old they are)
http://download.sears.com/own/00925737e.pdf

That being said, check the videos out, perhaps can get it to work after all for a while longer.

The charger for the dewalt 18V battery.
http://www.ezbuybatteries.com/dewalt-72v-18v-battery-charger-universal-replacement-13821.html

good luck I rigged a black and decker from walmart so far it works it has 2 outputs and the 2 pegs on the edge of the batteries take the juice. It saves about 100 bucks cause you can pick up a b&d charger for 25 bucks.

generally 1 hour and there are indicator lights on the charger to notify you when charging is complete.

You can contact a Dewalt Service Center to see if they have the diagram. Black and Decker is Dewalts lower priced line. A quick search on their website did not reveal anything. They may not have the diagram. As far as I know there are no parts available for the chargers so you may have a hard time locating the diagram. Try giving Dewalt a call.

sounds like the batt as had its the same prob as i had with mine to give it a bit of life so it will charge get hold of a bigger batt and two bits of wire and connect the + to + and - to - and it should charge but it prob will run down quick

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