I use the nimh's with my Dinotte taillight & they work fine in similar temps. I can't say that I've tested how long they will last, as I usually just charge them daily. Since Dinotte sent me an extra charger & batteries, I have both the Sanyo Eneloops & the energizers. I can't say for sure, but the Sanyo seems "smarter", the batteries don't heat up and the charger doesn't go by a timer as the energizer instructions said it does, it seems like the sanyo can tell if the batteries are fully charged.