It's better to have a car charger for your flashlight batteries like the RCR123, 16340, 18650, etc. instead of a charger for the whole flashlight in the car like my Stinger XT. Made an spare/extra 3-cell sub-C NiCD battery and installed a homebrew charger for the Stinger XT, instead of installing its charging cradle in the car. When the Stinger XT's batteries go weak, I take out the original sub-C battery and charge it in the homebrew charger. I then put the spare sub-C battery into the Stinger XT so I can use it immediately, no down time due to charging.
With today's RCR123, 16340, 18650 powered flashlights, we can buy a car battery charger that plugs into the cigarette lighter socket so when the batteries in the flashlight go weak, we just put the weak batteries in the car charger and then put the fully charged spare batteries into the flashlight for non-stop use.