I bought a used Mini cooper countryman 3 years ago. Since I've owned it when the weather hits around -5 degrees F and I cold start the car, the heater won't work properly. The dash says it's slowly building up blower speed as the engine warms up but nothing is actually coming out the vents. When the weather warms up to around 5 degrees it miraculously starts working again. If I let the engine warm up I'll get residual heat coming from the vents to thaw the windows, but no actual blown heat. If I try and drive it like this the windows often frost up obstructing my vision. When the car eventually runs long enough to warm everything up (2 hours or more) the heater will start working. I've talked to the dealership a couple times and every time they've said it's a battery issue, in the cold the battery strength is lower than it normally is in warm weather and the car shuts parts of the car down to save electricity. I've had the battery tested and they say it's in perfect shape.
I'm told it has some sort of an alternator style battery that slowly charges the battery as needed, and I'm hitting some sort of sweet spot where it's doesn't charge enough to allow the heater to work, but not enough to realize it's a problem. They suggested installing a trickle charger which for the first couple of years I didn't have consistent power to plug into. Too many roommates had to park down the street. New living circumstances, I can now plug it in every night, but it's getting cold again and still no heat. I don't think it's the blower, thermostat, or anything like that (I wouldn't say I'm even close to a mechanic however). In warmer conditions everything works perfectly. Any suggestions on What the problem could be, or even a work around. I'm thinking of trying a battery blanket, but the battery is in an enclosed spot that I'm not sure I can easily accomplish this so I'm hoping for a better solution.