[notjulianjaynes]

There's really only a handful of battery voltages used across all manufacturers. It makes more sense if you think about the series count of a battery pack instead of the advertised voltage. A single lithium ion cell will have a nominal voltage of 3.6v and a "Max" voltage of 4.0v (technically 4.2v, but you can extend the battery life by not charging to 100% capacity).

Thus a 10.8v (3 x 3.6v) and a 12v (3 x 4v) are the same thing, just measured differently.

As is an 18v (5 x 3.6v) and a 20v "Max" (5 x 4v).

36v and 40v are both 10 cells in series.

Etc.