Have you looked at the Milwaukee 12V? Not as tiny as you may want, but looks pretty good. Dremel has a tiny 4V and there are lots of generic "Chindia" tools of unknown power, runtime and quality. ( but I can guess) Amazon returnable may be your safest bet to fid a workable one.
I have wondered is a cordless rigged with a cable so the battery was on a belt hook would be potable and convenient enough.
Yes Gene, if your old one was Ni-Can, the new ones are far better. Every few years they figure out even better ones. There are some coming that are safer than Li-Ion and higher density that may work in cordless but not scalable to cars.