My 18v inpacter works fine with one battery but keeps stoping with the other when I try and use it

Seems batteries have completed their normal life and require replacement. Keep in mind that when batteries are exhausted, their voltage remain normal but loose current. It seems that batteries do not sustain current i.e. have become un usable.

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

May read instructions and see if charger is compatible of charging the two types of batteries you are charging ,,,,I have 32 dewalt 18v dc9096 batteries and 1d dewalt 18v dc9099 battery

could be 1 of 2 problems, the motor or the switch, I would think more the motor. you can get some idea of what the cost would be by going to dewaltservicenet.com and typing in your model number for the parts listing. But also keep in mind that Dewalt has a MAX service rate that they will rebuild the tool up to the MAX rate for it, that includes batterys (or it used to include them)

Batterys are not necessarily universal even withing voltage ratings by make and model. A bone of contention for many users for many years.

Rigid and Ryobi are two companies that have use standard batteries for their tool line. Consider this when making future tool purchasing decisions.

Thanks for your interest in FixYa.com

Hardware. Check the power source, the 18v is used only for the LNB.

I have the same problem and its about a year old too.

Plug in the charger and then being careful to only touch one contact with one lead use an ohm/voltage meter to check the voltage and see if the charger is putting out any voltage.

i think the trigger controls this

Try a new battery it sounds like a faulty battery