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Q: New battery won't hold a charge. 2000 Ford Ranger

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My truck died without much warning two days ago. I had an oil change done the previous week and they mentioned my battery was running low. So I assumed that was the issue and installed a new battery. Then last night, 24 hours later, the battery is dead again. I've had the alternator replaced within the last two years...so thinking it can't be that. Also, I checked it again this morning and my truck started right up and the battery meter read perfect (did the same thing yesterday when I started it up, but gradually lowered over the day). So seems like my battery isn't charging while I drive, but does somewhat while parked overnight. Any thoughts on what it might be?

My car has 155000 miles.
My car has an automatic transmission.

Hi there - this behavior sounds more like there is a parasitic load, or drain, on the battery after shutting it off. This problem can be diagnosed by connecting an ammeter to the positive (red) battery cable, observe the current drain (likely less than 1 amp), then, one at a time, remove each fuse, check to see if the current drain has dropped to near 0, then reinsert the fuse. This process should identify the faulty circuit in most cases. The specific components on that circuit can then be checked for current drain problems. A professional mechanic, like YourMechanic, can come to your location, and perform this procedure for you, and replace/repair the failing component.

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