Is the Dewalt DE9108 battery charger suitable for charging Ni-Mh batteries?

Battery is either ni-cad (nickel cadmium), Ni-mh (nickel metal hydride) or Li (lithium ion)
I do not know what the original battery was. You may be able to obtain a Li version but may need a different charger as charging rates for each type vary.

you cannot use any charger that is not used to charge ni-mh batteries car batteries charge at a rate of 5 amps minimum and if you do it will cause serious damage to the charger and batteries
if you want ideas , talk to a battery shop but unless it is designed to charge 14.4 volt ni-mh batteries-- forget it

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

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

Yes you can. On tools, 18 volts is 18 volts. Tools don't 'know' how the power is being created, either by Ni-Cad or Li-Ion means. Chargers are totally different. Most Li-Ion chargers can charge older Ni-Cad and some Ni-MH batteries but older Ni-Cad chargers will charge Li-Ion battery untill they overheat and sometimes start on fire because older chargers can't detect when the Li-Ion batteries are full.

Lithium Ion batteries don't charge the same way ni-cads or ni-mh do. You need a lithium ion specific charger to charge them. (Some chargers do multiple types.)

If the battery has been used a lot or has not been kept charged up it likely is shot. A battery that is not used a lot should be kept charged. I keep my battery operated drill on the charger almost all the time. I have two and change them once every two weeks. Several years old and they both work good.

There are basically 3 types of chemicals currently being used for cell phone and laptop batteries. Ni-cad, Ni-mh and Li-ion. There is a fourth makineg its way in Li-ion polymer. A couple things are consistent for all types of batteries no matter what chemical is inside. You must initially give the battery a 12-14 hour charge on the home charger. (Don't use a cigarette adapter for the first charge. This conditions the battery and don't take it off the charger that first time even if the charging indicator says it's full after 3 hours. Also the manufacturer's also state to run it thru 3 charge cycles. What that mean's is that you fully charge and fully drain 3 times. 1 full charge + 1 full drain = 1 charge cycle. Here's where the way you charge the battery starts to differ.

Ni-cad: Mostly only on older devices, has a "memory" effect, should be drained before a full charge is put on it, should be removed after overnight charge or can be overcharged and burnt out.

Ni-mh: Still used for some devices, has slight memory effect but not enough to have to fully drain before the recharge, should not be consistently left on charger after full charge that can eventually burn out battery and shorten usage time.

Li-ion and Li-ion polymer: Used on a lot of newer devices, has no "memory" effect, should be recharged as often as possible, actually likes to be charged and draining it regularly can cause the usage time to be shortened, can NEVER be overcharged so whenever you're near a charger put it on there. Besides those benefits a li-ion battery is lighter and smaller but the chemical can hold more charge than Ni-cad and Ni-mh.

So the one reply to your question said to error on the side of draining the li-ion batteries. This is incorrect information. You want to charge the battery before it gets below a 20% charge. Also batteries will not go bad from accidentally doing the incorrect charging procedure here and there but normally follow the correct procedure. One last note try to use the home charger more often than the cigarette lighter charger for best long term results. Cigarette lighter chargers do not give a full charge (about 95%) which in the long run can damage any type of battery listed.

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.

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