This winter, for the first time, I encountered the problem of battery failure at -25, after 2 days of inactivity. I bought it during the day, started the car in less than 2 seconds in the evening. Auto Nexia n150 volume 1.5. As I understand it, if it didn’t start in the cold from the first - the second attempt, then it’s better not to force it, but connect this device and start normally. The most important thing is to keep it warm, otherwise it's of little use. And after starting, immediately disconnect the terminals from the battery, because it does not give a weak voltage and you can set the contacts on fire.