I have a 2023 Chevrolet Spark and two weeks ago I noticed the battery was draining quickly, but when I take the car to the shop the alternator shows normal voltage. Could it be that the battery is internally damaged or is there something else I'm missing?
If the alternator is working fine but the battery is draining quickly, the most likely issue is that the battery has internally damaged cells or is reaching the end of its lifespan, though there could also be a parasitic drain (something that keeps consuming power when the car is off). I'd recommend getting a load test done on the battery at the shop to confirm whether it holds voltage under load, and if possible, check whether any accessory or component is draining the battery while the engine is off.
A battery with the alternator working correctly can still keep draining for several reasons, and it's not always the battery's fault. First, an aging battery loses capacity even if it technically works - it's like internally it has weak cells that can't hold a charge the way they used to. But there's also parasitic drain that people don't think about: there are car components that keep using power even when you turn off the engine (security systems, control modules, dashboard clocks). In a 2023 Spark this shouldn't be a big deal, but if something's short-circuited or a module is damaged, the battery slowly gets depleted.
What I'd do is leave the car parked for a whole night and measure how much voltage the battery loses when nothing's on. If the drop is more than 0.1 volts per hour, there's a drain that shouldn't be there. Then, with the engine running at idle, check that the alternator charges at around 13.5-14.5 volts - if it's putting out much less or fluctuating, the alternator might have a problem that the shop didn't catch properly (quick tests sometimes miss intermittent faults). It's also worth checking the battery terminals, since they're sometimes corroded and simulate a bad connection. If all that checks out, then yeah, the battery is worn out and needs replacing, especially if it's been around for a few years.
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