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Signs of bad battery?
01-15-2013, 02:27 AM
Post: #1
Signs of bad battery?
Today I noticed that my battery didn't seem to have a whole lot of zip to it when I started it. About 3 hours earlier I had driven the car for 45 minutes so it surprised me when it seemed a bit labored. What are the signs of a dying battery? How do you test a battery? I actually have a $30 radio shack voltage tester that I use on computer CMOS batteries and what not. Could I use that to test it? Would it take like 2 seconds for the service station to test the battery? I really don't want to get stranded with a bad battery or alternator.
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01-15-2013, 11:07 AM (This post was last modified: 01-15-2013 11:13 AM by Rupe.)
Post: #2
RE: Signs of bad battery?
Signs of a weak battery include age. 3-5 years is typical for an aftermarket battery while 6-5 years is possible for certain premium and OEM units.

Other things to look at are connections not being tight, like right at the battery. On vehicles more than say 5 years old it may be wise to follow the bat cables to the other end and check for good connections at the block and starter. Poor connections can cause low charge rate at the battery and odd voltages in the system.

The health of the charging system is directly related to battery life.... and you can't do a proper diagnosis unless there's a known good battery (properly charged) in the system.

Here's what I would do. Place your meter on the battery and observe the "at rest" voltage. It should be about 12.5 - 13 volts. If it's not then read the above again. If the engine will start you should observe the voltage while cranking (9-10 volts) and after it's running. (13-15 volts) These are within the normal range.

Low cranking voltage usually means one of several things. Either poor connections or a weak battery, although on an older car the starter itself can be at fault, or the battery might be ok if it's allowed to be properly charged after tightening connections. You will need to make the judgement call since you have not given us enough info on the car type or age.

Voltage after the engine is running is another factor. Too low and the battery will not be fuly charged. Too high and the battery may be damaged in the long term, but can act weak during a test.

Please report back with your findings and we can go from there.

Edited to add: One thing I did not cover is the possibility of "phantom draw" where something is left on and drains the battery over a period of time. There are ways to check this but it's a bit complicated. The straight forward answer for the moment is to look around for things like the dome light or glove box light staying on accidentally. Certain aftermarket stereo systems can also draw after the key is off. Again, give us more info and we're glad to offer suggestions.
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01-15-2013, 06:09 PM
Post: #3
RE: Signs of bad battery?
Interstate MT-51 battery replaced Aug 2011. 2005 Honda Civic. This morning it started fine after sitting all night. I'm thinking maybe I didn't turn the key all the way around... maybe. I don't know. For now it's working fine. Unless it happens again I'm just going to say "if it ain't broke don't fix it".
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01-15-2013, 10:01 PM
Post: #4
RE: Signs of bad battery?
OK, good battery brand and the car is not so old either but I would double check the connection tightness just the same.... and it wouldn't hurt to throw your meter on it to satisfy curiosity. If nothing else you will at least see what "good" readings are for the future.

BTW, a quick test to see if the alternator is keeping up would be to run the engine at idle with ALL of the accessories on, including the rear defoger, blower on high, and the high beams. (that's about 50 - 60 amps) If voltage holds above 13.5 for a few minutes you are good to go.

At any rate, glad to help and let us know if you need more!
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