E-Key

[saread]

Of course, all things being equal, it's way easier to just stash a spare battery under the seat.

Wallet is better ... keeps it out of the heat.

Fair point. Maybe not my wallet though.  I'm not sitting on anything lithium ion, ever.  I still don't understand people who put their cell phones in their back pocket and don't mind sitting on it - cue my wife. Shorted lithium ion batteries are ugly.  Even small ones.  Not going to risk a mini-Tesla incident anywhere near anything I consider sensitive.  Call me old fashioned (at least it would be something less profane than I'm usually called).