Thank you for the replies!
I haven't figured out how to multi quote on this forum, so I'll go down the line and address responses as best I can.
@ dukecola: this was not warm, it was hot! The outer insulation on the extension cord was tacky to touch from the heat.
@ ESokoloff: The bike's receptacle is fine, as is its charge cord. In the past, when charging at home the cord and the male connector on the bike have just gotten warm. Just to verify, I plugged in at home yesterday, nothing got hot. I plug in to a switched receptacle, so the cord is in as new condition.
@ heroto: "hospital grade ends" means they look great in pink scrubs.
I misspoke, prolly should refer to them as commercial grade. Our electricians make these extension cords up for us at work. They're over-built for rough service.
@ NEW2elec; Thanks for the tip. I already bought a new extension cord, 12/3 25'. I would be afraid to us one with 14 gauge wire. I panicked and stopped at the Home Depot on the way home from work Friday, and bought the best 25 foot cord they had.
@ DonTom: "Nope". I like that. I'm going to be optimistic, no damage done! Good stuff Don, thanks. At work, I always plug the bike's cord into the extension cord, then plug the extension cord into the outlet. At home the bike's cord plugs in to a switched outlet. Since new there hasn't been any arcing at the bike or its cord.
@ evdjerome: A 15 footer is all I really need at work, but the Home Depot only had 25' so that's what I got. I have heard the same thing about loops and coils so I avoid them.