How reliable are the Battery Hydrometer testers in testing car battery cells ??
I've just tested my recharged overnight battery & the results don't always seem consistent.
The tester has 3 ranges: Good/Fair/Recharge
At first tester showed 2 Good cells, 3 Fair, 1 Recharge
Later on it showed 1 Fair, 5 Recharge
I tried number of times, made sure the rubber was sealed around glass.
The test results don't seem consistent.
How reliable are these testers, what have people found ??
(My battery went flat, not sure why as I did long trip (150 miles) few days before so should be well charged, hardly used car since & am sure didn't leave lights or anything major on, alternator is working as checked voltage).
Typo corrected. I assumed you meant 1995, as per previous questions on your Cavalier? - which you seem to have omitted from the drop down menu again; now added once more
Edited by Webmaster on 08/08/2008 at 12:38
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The acid density was lower on the second test because the battery heated up when you charged it. To achieve a useful result you should let the battery cool to ambient temperature for 12 hours and then apply the appropriate density correction for temperature.
Having said all of that, if the electrolyte level is correct and your alternator gives 14V or a bit more when under load (increase speed as required) then your battery probably requires renewal. As a rough guide, at present UK temperatures the acid specific gravity for a charged battery will be about 1.28.
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Both tests were just after I stopped charging the battery within 5 minutes of each other.
I assume the 1.28 would show as Good on the battery tester.
I'm not sure why my 2 tests after charging would not be reasonably consistent.
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If you test soon after charging there are minute bubbles in the sample and fool the reading as well as being warm. If the battery is charged then connect a head ligh bulb across the battery and leave if for an hour and check, then leave it another hour and I suspect it will be looking sorry for it's self. You could of coarse pop it back into the car and drive round to your local car accessory shop and ask them to test it. Most use a pulse discharge system which checks the internal resistance and capacity and take 5 seconds. Regards Peter
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Specific gravity readings are only valid providing no acid has been spilled or not to much water has been added.
As mentioned in an earlier post, providing the voltage across the battery terminals is about 14 volts with the engine running, its charging OK, if its going flat either something is discharging it, or more likely it needs replacing.
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If you do end up having to buy a new battery then try your local Vauxhall dealer as you may be surprised to find that they are cheaper than Halfords etc & will have the exact spec of battery, of course.
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