I have the Dremel 8260, but it's the same battery. all Bosch Professional 12V devices also have the same battery, they are universally compatible (bosch and dremel)

This battery fits the Dremel 8240 and 8260. The Dremel Lite has a built-in battery.

However, the Dremel batteries also fit the 12 volt Bosch Professional (blue) series.

So does this also fit the Dremel 8240? (That would have been my question...)🙈