Best bet is to get a corded too, don’t store the LiIon fully charged when it isn’t going to be used in a while, battery lasts far longer, not fully charging or leaving on charge is best...longer life from batttery.
Your old worn out Dremel can have new bearings installed and it run much better as well as a new set of brushes. Clean it out of all the carbon dust and clean up the slots in the commutator. Polish the brass commutator and if it is grooved badly, thenn yes, time for another, otherwise clean and slowly run it for several minutes to set the brushes before you use it and take it easy on the revs until the brushes are fully seated.
I like the regular corded models and use a flex shaft a lot... essential if trying to touch up ports if porting, die grinders with long nose are the way to go on die grinder and spending more for one that has good speed and power but low CFM usage...
Don’t buy cheap brass brushes for the Drexel and never run them above 15k rpm, the start shedding wire which can give you a nasty eye injury and they hurt when embedded in the skin, know first hand on that one. Cleaning brushes with some spray cleaner that evaporates fast and lightly oiiling steel tools after use. Oven cleaner can cut through build up on cutters but neutralize it and oil if steel.
Use a Dremel a lot. Or have...not as much lately.
