Bad alternator, or just a regular dying battery?

Question

The battery in my car is dead, and I'm not sure whether it's the alternator's fault or just the natural death of an old battery.

Vehicle: '04 Honda Accord. The alternator was replaced 4 years ago. As for the age of the battery, I admittedly don't know. I know it was about three years old when the alternator was replaced, and I don't recall replacing it since then, however, I may have and just forgot about it. The date is not immediately obvious on the top of the battery.

About three weeks ago I noticed the battery light intermittently flickering on and off. The last time I saw this light it was a constantly-on indicator light when the alternator was failing (ran for about 45 minutes then died on the roadside). The light would come on at random times (some times it would come on when I slowed down, some days it would come on when I turned left, etc.) It was only ever on for a few seconds at a time followed by long periods of not being on (minutes to hours) but seemed to get worse if I used the car for short distances.

My initial suspicion was bad wiring, and the top of the battery was corroded, after cleaning the terminals the light came on less frequently, but worsened again.

I went away for about 10 days and didn't drive the car, when I returned the car was very slow to start and when driving it the accelerator didn't work. (Pressing the accel down the RPM slowed and the lights dimmed, I was only able to drive by taking my foot off the accel and just coasting and braking.). On occasion the engine would rev and work for a moment, but was unreliable. I managed to get the vehicle home. The battery light was NOT constantly on, and was off when I was having acceleration issues. After turning the car off it would not start again. It's evidently a dead battery now.

The car stereo has been dead for years, so I didn't notice any symptoms from that. The cabin fan has been dead since winter (bad blower motor resistor I haven't gotten around to replacing), so I don't know if the AC system would have caused any problems had it been on.

Answer 1

An 8 year old battery is definitely due for replacement and could very well be the issue.

A quick and easy way to test the alternator after you have installed the new battery is to use a volt meter. I used to work at Interstate Battery and we would do it after every battery install to make sure the new battery would be getting a proper charge. You simply put the two leads on the correct battery posts (positive to positive and negative to negative) and check to voltage with the car running. A fully charged battery (which your new one should be) will sit at around 12.8 volts. With the car running and a proper functioning alternator that voltage should read between 13.6 and 14.5 volts. If the voltage is lower than this there is a good chance that the alternator is failing.

Answer 2

The answer was both. The battery had died and died short, which over time messed up the alternator. I was fine for a while because the alternator only acted up at high heat. Had to replace both the battery, the alternator, and the battery wiring (too badly corroded to get off the old battery.) The moral of the story is to change your battery from time to time, I suppose.

Answer 3

Pull the battery, take it to a shop and ask them to perform a discharge test. They might want to keep it in to charge it overnight, or you might want to charge it with an external car battery charger yourself. If the battery passes the discharge test, then you could have a faulty alternator.