So, I've been running into some issues with starting on cold mornings—the voltage drop from cranking is enough to turn off all the cabin and dash lights. Ordinarily, I would have thought 'well, time for a new battery', but I borrowed a battery tester from Autozone, and at the battery, the voltages are fine both sitting there and under load—certainly not bad enough to turn everything off.

Possibly related: when I start the car in cold weather, the speedometer rattles around 0, making a buzzing noise, before settling down once the car has started.

I might have guessed ground straps, but that should have shown up during load testing on the battery, right? The terminals at the battery side are in basically perfect shape, and the battery is only as old as my ownership of the car, so two and a half years or so.

 

What was the voltage that the battery reader said? Any codes present in the system? The buzzing has been said to indicate a bad battery. Check out this NAM thread HERE where the issue turned out being a bad positive terminal cable.

 

No codes. I don't remember exactly what the voltages were, but it was in the green range on the tester--dipped a little below 12v on the load test, IIRC.

I tested at the battery in the trunk, though. If I test between the positive terminal under the hood and ground, that should show different voltages from the battery if the cable is bad, right?

 

A normal battery should read a voltage above 12 volts with the car sitting still, and no electrical devices on. (Don't worry about the door lights, they hardly make a dent). A typical reading would be in the 12.6-volt range when the battery is fully charged. If the reading is 12 volts or less, then the battery needs charging or needs to be replaced with a new one. I have seen instances where individuals reported a bad battery at 12.2 volts. Most of what I have seen points to signs of a battery going bad. Some have pointed out that it's a quirk as well. Some more info HERE.

 

I would check the terminals at the starter and follow them to the battery, put some glasses on and then unplug both terminal and reseat them on the battery post, takes a 10mm socket and wrench. Watch not to over tighten them. Do you have a factory or aftermarket battery, sometimes the aftermarket ones the post are a hair smaller. I had a bad battery ground terminal on the r52 MCC and it had a weak connection.

 

Thanks for the tips. Further testing showed that it was indeed the battery—it was borderline when I tested it at 40F, and insufficient this morning at 5F. New one seems to have cleared it right up.

 

You're welcome. Great! Glad that was your issue and things are all fixed up. Now time to enjoy the MINI once again.

 

Great, glad i could help.