I too am in construction and use all the Dewalt tools... I have 2 of the impact drivers, grinder, circular saw, sawz-all, hammer drill etc....
A while back while cruising on flea-bay, I found a guy selling a "secret" on how to revive a rechargable battery... his "secret" only cost $8 with shipping.... I took the bait, well, cuz curiousity got to me....
his "secret" is to take your dead, wont-take-a-charge battery... and hit it with "up to" twice the voltage for 3 seconds... to "wake it up"
I used a 9- volt milwuakee battery that has been setting dead for 10 years and hit it with only 12 volts from a car battery (for 3 seconds). IT WORKED!!!!!! for a little while. I figured that it didnt work perfectly cuz it had set for 10 years dead. but it still worked.
the way to do it like he explained was to hook up the negative of the dead battery to the negative of the source of your higher voltage. then to "flick" the positive against the dead battery a couple times (2 or 3)
then just hook it up to your charger and away you go!!!
I actually hooked up that dead 9-volt battery to the 12-volt car battery for 10 minutes.,... and now it will run the drill for almost 8 or 9 minutes at a time... but I wouldnt recomend this... it could blow something up.