12V DC vs % Battery Charge

[richardcoxid]

A question for all you 12VDC Battery Gurus,



I have 4- 6V deep cycle Golf Cart batteries connected in series/parallel through a Perko battery/isolation switch with “Both, Batt #1, Batt #2 and Off” positions.



After4 days of charging (Progressive Dynamics, Intellipower 9200 series, 60Amp. “Smart” Converter) All readings are open circuit and both batteries were isolated (Off) during the idle time.



Secured charging, initial voltage was Batt #1- 12. 9, Batt #2- 12. 94, 100% charge



19 hours after securing charging Batt #1- 12. 43, Batt #2- 12. 45, about 75% charge



4 days after securing charging Batt #1- 12. 39, Batt #2- 12. 39, about 70% charge



2 weeks after securing the charge the voltage had about stabilized, Batt #1- 12. 33, Batt #2- 12. 35, about 65-70% charge.



When I lost about 25% of full charge after just 19 hours of idle time (open circuit) and another 10% or so after 2 weeks I think that my Batteries are shot! What is your opinion?



Thank you for your advice and time!!!

 

[jelag]

When I took a DC electrical class in college we were taught that high levels of moisture and moisture under the battery would/could contribute to discharge. One of the lab experiments we did was spray the top of a battery with water and we'd put one lead of a volt meter on one post and run the other lead on the top of the battery close to the other post and you'd be able to measure voltage from the battery starting to discharge. . we'd do the same test with salt water...

I'm not sure you really have a battery problem until you can eliminate the normal discharge from that moisture...

Today I pulled off the floor (sitting on a piece of plywood) a battery out of my bil's truck that is now 11 years old, we'd changed it 60 days ago... and I'd traded in some junk and kept his batteries for my own use. . I threw a digital volt meter across it today and it was down to about 40% charge... I put it on a trickle charger and will use it tomorrow...

I personally think your batteries are OK... but would love to hear other comments. .

 

[Newt]

A question for all you 12VDC Battery Gurus,

I have 4- 6V deep cycle Golf Cart batteries connected in series/parallel through a Perko battery/isolation switch with “Both, Batt #1, Batt #2 and Off” positions.

After4 days of charging (Progressive Dynamics, Intellipower 9200 series, 60Amp. “Smart” Converter) All readings are open circuit and both batteries were isolated (Off) during the idle time.

Secured charging, initial voltage was Batt #1- 12. 9, Batt #2- 12. 94, 100% charge

19 hours after securing charging Batt #1- 12. 43, Batt #2- 12. 45, about 75% charge

4 days after securing charging Batt #1- 12. 39, Batt #2- 12. 39, about 70% charge

2 weeks after securing the charge the voltage had about stabilized, Batt #1- 12. 33, Batt #2- 12. 35, about 65-70% charge.

When I lost about 25% of full charge after just 19 hours of idle time (open circuit) and another 10% or so after 2 weeks I think that my Batteries are shot! What is your opinion?

Thank you for your advice and time!!!

You have 6 volt batteries. You need to test a 6 volt battery, not 2 6 volt batteries. A bad battery can drag the other one down.

Newt

 

[Road Dog]

Measuring the voltage doesn't tell you much. Right after charging the surface voltage around the plates is higher than the rest of the cell. The battery has to sit for a while to get the true voltage. A small load helps too. This chart gives a better volts vs charge indication. Fully charged is 12. 6V and discharged is 10. 5V.

If it's a wet cell with caps then you can measure the specific gravity with a hygrometer and that gives an accurate state of charge. Load testing gives a better indication of the health of the battery too. The only way to measure the capacity is to load test over time.

My smart charger provides the same voltage/%charged but I don't find it useful.

 

[TLane]

I agree, measuring battery voltage doesn't tell you much. Plus, you have to measure the battery temperature and adjust the voltage reading to be anywhere close to state of charge. A hygrometer can be purchased for a few bucks from Napa, probably others as well. Be sure to get one that has the built in thermometer for adjusting the specific gravity. But the real test is as Road Dog says, load test it over time.

Don't believe those little electronic boxes that the battery stores all use that test a battery. They are full of tricks and electronic wizardry, but practically useless for checking a battery. A light bulb is more useful, but it takes more than a minute or two to really test a battery.