I have a cordless and a corded. The corded stays in the garage where I am likely to need the extra power, cordless is in the basement shop. The batteries (Lithium) in my cordless are still fine after many years.
What brand & model ?
My cordless Dremel is basically a paperweight. Several hours of charging for 5 - 10 minutes of light duty work. Although it is so old that the unit is no longer made. And forget about finding the NiCad batteries.