Battery Testing Procedure

[jmseas]

It's time for new batteries, I think?
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Anyone have suggestions for a battery testing procedure? I'd like to 'demonstrate' that my batteries are ready for replacement...

&Thanks to everyone's recommendations, I have a new Victron BMV battery monitor to assist in the test. I really don't want to pull them out and bring in to a battery shop so I'm hoping someone has developed a simple procedure to test?

I'm guessing it would go something like this: fully charge, rest, draw 1 amp for 20 hours, rest, measure voltage, compare to fully charged voltage.

thanks,
John Mc..

 

[Benny17441]

The best way to determine when a battery is ready for replacement is at the first sign of problems. I have had batterries that empirically had been demonstrated to have a diminished storage capacity and would not hold charge much beyond 90% but continued to perform flawlesly for more than two additional years after being tested. The minute they failed to provide my defined threshold of adequate performance that is when they were ready for replacement. Test results by themselves do not mean anything, you have to set a threshold of what is adequate and what is not and the numbers will not tell you that. Only observation and practical experience based on your needs.

 

[mitiempo]

The best way to test a battery for capacity is to first charge it fully. Take the AH rating and divide by 20 as deep cycle batteries are rated at the 20 hour rate. Apply a load equal to that number and time how long it takes to reach 10.5 volts. A perfect battery will take 20 hours - the less capacity it has the shorter the time to 10.5 volts.

 

[centerline]

testing a battery.... you can load test it with a carbon pile tester.... using the proceedure for either a deep cycle or a starting battery..... but there is another way.....
the other way to tell if the battery is beginning to fail is quite simple and more accurate...... get a good quality hydrometer. the little fluid tester with the squeeze bulb on it for batteries.... a good one from the battery store costs about the same as a questionable one from the autoparts store.
then charge your batteries completely.... then unhook them from the system by disconnecting either positive post or negative post..... unhook them, not just by shutting the switch off. then wait overnight or a week or a month, whatever.... then using the tester, check the specific gravity of each individual battery cell.... any cell that drops below the fully charged mark is getting weak..... you can find a bad battery this way before it ever shows any symptoms elsewhere..... the longer the wait after disconnecting the batteries, the more accurate the test. actually 24 to 36 hours is plenty of wait time.... reconnect or replace as necessary....