Is this battery dead?

[lumphammer]

I have charged two batteries using the same charger for the same time. Three days later the new one is still at 12.9v, the old one has now dropped down to just under 12.6v.

Is this battery dead? Is there anything that would revive it?



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[William_H]

The best way to test your battery is to see if it will do the job you want it to do. After charging connect it to your engine starter and check if it will start the engine give it a reasonable test with stop control operated (diesel) or plugs disconnected petrol. Next discharge it with a light bulb or string of light bulbs if at home or general boat load iof on the boat. Check the current being drained and monitor the voltage until it falls to 11 volts. For a good battery this should be better than 50% of the rated AH. Amps multiplied by hours discharged. You can decide from these tests if it is dud.

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[nickjaxe]

I use a hydrometer on mine seems to give me a good idea of its state and they are cheap.

Nick.

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[VicS]

12.6volts after resting for 3 days would suggest that the battery is well past its prime but not completely dead yet. It would almost certainly perform satisfactorily in a situation where it was in near daily use, in a car for example, but you may well find find that if left for a week or two it will have lost so much charge as to be virtually useless. Having said that the 8½ year old battery in one of my cars is currently showing 12.55v after standing for at least a couple of weeks and I don't expect any problems at the moment. If it were standing outdoors in mid winter that might be different.

I would try charging it some more, for how long will depend on the type of charger you are using, and test it again. You may get another season's use out of it or you may not. If this is one of a two battery installation its worth giving it the benefit of the doubt for a while but if this is the only battery then probably not especially if the new one you mention is intended as its replacement.

I am not a great fan of hydrometers for battery testing. One would identify a dead cell but then what, you can't replace one cell.

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[Rick]

Not quite clear from your post - were the batteries paralleled together while charging? If yes, then a battery with higher resistance will not necessarily get any charge, but still be usable - that's why pairs of batteries should be bought together - try charging it by itself.

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[david]

At 12.6v Not really

Battery Testing can be done in more than one way. The most popular is measurement of specific gravity and battery voltage. To measure specific gravity buy a temperature compensating hydrometer at an auto parts store. To measure voltage, use a digital D.C. Voltmeter.

You must first have the battery fully charged. The surface charge must be removed before testing. If the battery has been sitting at least several hours ( preferably at least 12 hours) you may begin testing. To remove surface charge the battery must experience a load of 20 amps for 3 plus minutes. Turning something on with a heavy load will do the trick. After turning off the heavy load you are ready to test the battery.

<pre>State of Charge Specific Gravity Voltage

100% 1.265 12.7
*75% 1.225 12.4
50% 1.190 12.2
25% 1.155 12.0
Discharged 1.120 11.9</pre>


*Sulfation of Batteries starts when specific gravity falls below 1.225 or voltage measures less than 12.4 (12v Battery) or 6.2 (6 volt battery). Sulfation hardens the battery plates reducing and eventually destroying the ability of the battery to generate Volts and Amps.

Load testing is yet another way of testing a battery. Load test removes amps from a battery much like starting an engine would. A load tester can be purchased at most auto parts stores. Some battery companies label their battery with the amp load for testing. This number is usually 1/2 of the CCA rating. For instance, a 500CCA battery would load test at 250 amps for 15 seconds. A load test can only be performed if the battery is near or at full charge.


<hr width=100% size=1>David<P ID="edit"><FONT SIZE=-1>Edited by david on 21/07/2004 07:50 (server time).</FONT></P>