Joined: Aug 2010
Posts: 12,728
Likes: 2,105
From: Madison, WI
Bikes: 1961 Ideor, 1966 Perfekt 3 Speed AB Hub, 1994 Bridgestone MB-6, 2006 Airnimal Joey, 2009 Thorn Sherpa, 2013 Thorn Nomad MkII, 2015 VO Pass Hunter, 2017 Lynskey Backroad, 2017 Raleigh Gran Prix, 1980s Bianchi Mixte on a trainer. Others are now gone.
You should not charge Li Ion batteries below freezing temperature. But I suspect your light warmed up pretty fast when you got it inside, so it was probably warm enough to charge once you started charging it.
I am surprised the light had roughly 60 percent performance (15/25 miles) at below freezing. I would have expected less than 50 percent.
If you have your phone on during that time and if your phone is not kept warm, if it was running apps and had the screen on, that battery drains fast too.