Battery diagnosis

[WmWatt]

My battery was fine yesterday but would only crank the engine slowly today, then not at all. I got it started once but then nothing. The built in hygrometer was green which is supposed to mean the battery is fully charged. Putting a voltmeter across the terminals showed 12 volts. When I started the engine the voltmeter went to 13 volts, a bit low for charging voltage. The positive terminal had a bit of green on it so I cleaned it up. The battery was then charged for an hour on a 6amp charger. The charging amps went from 2 to 0.5 while the charging voltge went from 13 to 14.5. The car then started up fine and the alternator charging voltage was 14.5. Normally it takes about 8 hr to fully charge a dead battery at 6 amps. I let the car sit for an hour and tried starting it again. The starter won't turn. Again the battery appears to be dead althought the hygrometer is green and the voltage across the terminals is 12. I did a search of the Internet under "battery diagnosis" but did not find this situation and cannot understand what is happening. Does anyone understand what's going on here? Thanks.

[FB71]

first, never trust that "eye". It's only for checking BSOC (Battery State Of Charge) while the battery is in stock, waiting to be delivered. I have only seen about 10% of those eyes be accurate (I've dealt with thousands of batteries over the years, I even did warranty audit). It sounds as though you have a plate that has correded sufficiently to make intermittent contact with its neighboring plate. Relatively common issue in older batteries, especially ones that have been allowed to fully discharge (remember, 12.00v is a dead battery, 12.65 is 100% charged). Simply time for a new battery.

[WmWatt]

Since posting the original message I disconnected the negative cable and inserted an ammeter. There was no current so I assume there is nothing in the car draining the battery. After 1 hour the voltage across the terminals had gone down to 12 volts again and the engien would not turn over. So I put it on the charger again with the amps going from 2 to .5 same as before and the car started right up. The battery doesn't seem to want to hold a charge. I'll take the battery out of the car. I bought it second hand and it has been in the car since January of 1998. I only use the car 1-2 times a week and was toppign up the charge once a month utnil this year. Before putting in a replacement I'd like to be reasonably sure it will not go dead right away due to some problem in the car itself.

[georgeb]

It was bought 2nd hand and it's been in there since Monica Lewinski?

[walth]

5 years is "good" for a battery...13+ is a miracle

[georgeb]

Don't trade that battery in. Donate it to the Smithsonian.

[iceracerdude]

Listen, do yourself a favor a pick up one of these:

This is a picture of a 100 amp unit, and you can get this at harbor freight for $20 all day long, less if you print up a 20% off coupon!
You can do three tests with it and it will stop you, and others, from miss diagnosing the differences between bad batteries, starters, and alternators.
It will test: the battery, the alternator output, and even what the starter draws when you use it!
In my case the "others" are always what I refer to as "sentimental" friends and family members who want to hang onto their batteries for years
longer than the factory suggested life of it ha, ha.
The only problem with it is, It takes as long as 1 min. to use! Well 2 min. if you keep it stored in the box it comes in, like I do.

[Clay]

I agree with FB71 that there is probably something wrong with one of the plates.

Problems like this and the battery is over 5 years old, it is likely the battery, especially since you checked for parasitics.

It is also a good idea to check and make sure the connections are clean and tight. I like to use battery terminal spray, and one of the best ways to clean the battery is probably a hose and some baking soda, just dont get baking soda in the battery.

If the battery is servicable, the plates should be covered with the electrolite. (I believe when the battery is in charged state, ie not dead) Make sure to don some safety glasses when messing around with batteries.

[getnpsi]

No guessing as the night time temps are not what they were a month ago. that HF tool is a good one, never have picked one up.

Its harder on a battery, but if you can start a car with the headlights on, it means its getting good contact and it's good to go. Bad contact will make bright headlights and no start condition, trust me i am very careless with terminals. So happy to get the car together and click...lol. I own 5 cars and they all have top post design, you think i really own 5 good batteries? Yeah right.

[WmWatt]

Thanks for all the comments. I replaced the old battery. The replacement battery was purchased at a garage sale in July 2006 for $20 and has been sitting in the garage waiting it's turn in the car. I've been topping them both up once a month pretty faithfully. The car starts fine with the replacement battery. I only drive the car 2k km a year, thats about 1200 miles so the battery isn't used much for starting.

[georgeb]

And I thought I milk the bejeezus out of stuff.

[iceracerdude]

The headlight trick goes like this by the way: You simply pull the headlights on for a few seconds (I know, what is a "few"? Well we know a couple is two for sure, and because "several" is probably like seven, because after all, it starts with an S, I'm going with five for a "few" you know because of that F and all) then turn them back off, THEN start the car. The reasoning I always heard was it warms the battery up a bit before you call on it for the really big amps those greedy starters require!?

Like I said earlier, the only reason I even have that testing tool is because I'm married now, That means I inherited a whole extra family of cars and owners that look to me for help on their stuff, because of course, they see how all my stuff runs/performs. My way of thinking on batts is simple, I buy very good ones based on the idea I'm really only spending like $10 a year on average. It's worth $10 a year to me for the piece of mind it brings on all my stuff especially my plow truck and my wife's Suv.
I miss the large selection of dual post style batts, complete with the built in handle that seemed to be more readily avail, but not so much anymore!?