I have a Camry that has been maintained regularly. The car battery is about 4 year old. 1) For the past 2 weeks, when I was to do a cold-start, it gives some cranking sound and engine shuts down in the end. So I have to step on gas to have the car moving. and once it is up and running, everything looks normal. 2) yesterday, I found all my radio channel have been reset. And when I was to have the car started, I see all the lights on dashboard were getting dim, as if the battery was dead, and head-lights were not working either. But funny thing is , when I check my car battery, it still shows Voltage of 12.41. And if I was to use external battery charger hooking on my battery, the car starts right away. Can someone give me some suggestions what might be the issue ? Thanks a lot.
Batteries have voltage and they have amps (simplifying a bit here). It's possible for a car battery to "go bad" in a way that will give a good voltage reading, but not have the power (amps) to do much work at all.
Another issue that can look like your symptoms is a loose or corroded battery terminal clamp. If the connection is bad, it will show a good voltage, but will seem to "die" as soon as a starting load is put on the battery.
So, check the connections and have the battery tested with a load tester. While you're at the parts store, they can probably check the alternator with their tester as well.