We have a ’95 Mazda MPV running Windows X… oh, wait. Sorry. It runs on gasoline. Or at least it used to. A couple months ago (after several months of sitting), I had to replace the battery. I then had it tuned up for good measure, it ran once or twice a week since then, and all seemed fine. Until a couple days ago. I got in, turned the key, and there wasn’t a hint of electricity. Not a glimmer. Nothing to the starter, lights, horn… nadda. I have no idea why. It’s kept in the garage with our car, so we know the lights weren’t left on, and the keys aren’t kept in it so none of the accessories could have been on.
The battery still looks new (i.e., there’s no corrosion under the terminals blocking a good connection). That’s about as far as I got. Now what? Do I just pull the battery, head down to Autozone to ask for a refund? Do I try and charge the battery? Jumpstart it? Do I automatically assume it’s the alternator, or is there some test for that I can do on my own?
It’s a second hand-me-down vehicle that generally sits and sits. We don’t drive it that often (though now I know better), so dumping more and more money into it isn’t a likely option.
Get a voltmeter somehow. If you can’t borrow one, buy one - they’re cheap. You can get a simple handheld digital voltmeter (DVM) for less than $15.
Pop the hood.
Set the DVM to measure DC voltage. If there are multiple voltage ranges, make sure you pick a range that is greater than 15 VDC.
Plug the red probe into the DVM’s positive (+) input. Plug the black probe into the DVM’s negative (-) input.
Stick the red probe on the battery’s positive terminal. Stick the black probe on the battery’s negative terminal. Read the voltage. Ideally it should be 12.6 VDC. If it is significantly less than 12.6 VDC - like less than 11 VDC - then something in your car is probably draining the battery. If it is not significantly less than 12.6 VDC, then there is a problem somewhere in your car’s electrical system. Most likely a bad connection.
If the open circuit battery voltage (when measured directly at the battery with your DVM) is O.K. - which means it is not significantly less than 12.6 VDC - turn your headlights on and measure the battery voltage again, at the battery. Also (with the lights on) measure the voltage between the battery’s positive terminal and a metal place on the car. Report back with the results.
The starting point is the battery. Check its state of charge (should read close to 12.6 volts). If it’s not fully charged, charge it. If the battery was fully charged, go to A. If it wasn’t, but after charging the vehicle now starts and things seem normal, go to B.
A) Remove the battery cable connections, clean them inside and out, clean the battery terminals, and reconnect the battery cables making sure to get them properly tight. If the vehicle now starts and things seem normal, it’s a pretty sure bet you have solved the problem. If it’s still acting up, it’s likely that the battery is faulty.
B) Either the battery is faulty (won’t hold a charge) or there is some electrical drain on it. Said drain could be from something accidentally left switched on (e.g. the dome light) or from something malfunctioning. To determine the former, carefully and thoroughly check all possibilities, such as a door not fully closed or the light switch not turned all the way off. Testing the latter (malfunction) requires equipment and knowledge beyond what most do-it-yourselfers have available (e.g. ammeter, wiring diagram, understanding of applicable trouble-shooting procedure).
While it’s not impossible that the alternator is faulty, it’s not the most likely suspect for the symptom described. I wouldn’t replace unless and until it had been proven bad through testing.
My first thought would be to jumpstart it and then drive the van down to AutoZone and have them check the entire electrical system. They should be able to tell you whether the problem is with the battery, alternator, cables or whatever.
I wouldn’t do that if the battery was completely depleted. The last time I gave someone a jump, the diodes in my car’s voltage regulator smoked a week later. Coincidence? Not sure. It can also cause the regulator in the car w/ the dead battery to smoke. (A lot of regulators nowadays are not designed to charge a dead battery.)
If you have a dead battery, and the dead battery has been dead for a while, you have two options IMO:
Try charging the battery using a stand-alone battery charger.
Buy a new battery.
If it’s been dead for a while, I always do #2. In my experience, a dead battery that has been dead for a while is not worth messing with.
This is good advice. Alternators are designed to top up and maintain the charge on batteries in a normally functioning systems. They are not designed to charge dead batteries, and will be overstressed if that is attempted.
So if my friend listened to the radio too long and her battery “died”, could it still have enough in it that I didn’t hurt my car when I gave her a jump?
…with pie!
I do have a battery charger and the battery is less than a month old. After putting it in, we took the van on wee hops around town (15-20 minutes) and even took it on a trip (~300 miles round trip). It showed no signs of faltering electronics until it just wouldn’t start – and the time between last use and non-starting was maybe a week and a half or so.
ETAsk:
Obviously replacing the battery is an easy task. What about the alternator? Is it pretty much a bolt-on part, or will I need special tools or need to reroute belts after removing a ton of other parts? Could it turn out to be a third thing?
Yes. Usually in that situation, while there’s not enough charge in the battery to crank the starter, there’s still enough to operate lights and such. What the OP describes seems to indicate little or no charge left. In the case you describe, getting her car started is unlikely to put significant stress on your alternator. However, getting her battery up to full charge could overwork her alternator, and the safest course is for her to have the battery fully charged by an external charger as soon as possible.