Riding in -20ºF? Phone App, with the phone in your jersey pocket, underneath (presumably) a parka, so your body heat can stop the battery from freezing. Things like electric cars have to use specially formulated batteries to perform below freezing-- the batteries in consumer electronics (like bike computers) are gonna be super unhappy when asked to operate anywhere near or below 0ºF. If you don't want to go the smartphone route, there's always the tried-and-true technology of yesteryear:



Doesn't care about heat or cold.