I think I know the answer to this.

Assuming it's not, what do y'all do to keep it dry? I only put it on when using it, and w/ my new 872 lighthead the total cord length is quite short.

The best I've come up with so far is putting a ziploc baggie around the battery before mounting it to the frame (cord doesn't reach my handlebar bag from mount point on head tube).

Inelegant.