The car won't start well in cold weather, the starter seems to be losing power. The battery is from 2024, it's new as far as I know. Even at +15 degrees it sometimes cranks slower. How can I figure out what exactly needs to be replaced?
It's most likely the battery, even if it's supposedly new - batteries degrade, especially if the car sits in the cold. I had a similar situation with a Kia: the mechanic checked it with a load test and it turned out the battery was putting out insufficient voltage under load, even though it looked normal at idle.
First try charging the battery fully with a charger - if the problem persists when it's plus fifteen degrees, then you need diagnostics with a load tester or a battery replacement. If everything's fine after charging, just charge it more often before the cold weather hits.
Try doing a load test on the battery - it'll take about 10-15 minutes at any auto electrician and you'll know right away if that's the problem. If the battery holds voltage under load fine, then it's definitely the starter; the armature might be burned or the brushes are worn out. And if the battery sags already during the test, replace it even if it's technically still new - in cold weather degradation speeds up and the battery can lose half its capacity over a few seasons.
Before you do a load test, check how the starter cranks right after the engine's been running - if it cranks fine then, the battery's clearly not holding a charge. If it cranks weak then too, it's either starter wear or bad brushes. In cold weather the problem gets worse because the battery's capacity drops, but that doesn't mean it's completely dead - a new battery from 2024 can just lose some performance from a deep discharge or a manufacturing defect.
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