Sealed Lead Acid Battery charging

salute2vishal

Joined Nov 1, 2012
1
I have a query regarding sealed lead acid battery.

· I am using 7.2 Ah 12 V sealed acid battery in our machine. Now if the charger is charging the battery and after some hours if the battery voltage measured by charger is more than 12.7 V and the battery charging current is less than 100 mA.
· So under this condition is it right to say the capacity of the battery now is more than 7.2 Ah or we need to really measure the battery capacity with some measuring instrument to really know that battery capacity has reached more than 7.2 Ah.
· This though has come in my mind cause I think that If the plates are damaged, sulfated, or partially gone from long use, the battery may give the appearance of being fully charged by showing more than 12.7 V and consuming less than 100 mA charging current in the battery charger display and still the capacity of the battery is very low.
Regards,

Vishal

crutschow

Joined Mar 14, 2008
24,735
If you really need to know the actual battery capacity then you will need to apply a load and discharge it at the 10 hour rate. The value of the load current integrated over time will give you the battery Ah capacity.

bountyhunter

Joined Sep 7, 2009
2,512
I think he meant to discharge the battery at C/10 rate to measure it's capacity.

I think that If the plates are damaged, sulfated, or partially gone from long use, the battery may give the appearance of being fully charged by showing more than 12.7 V and consuming less than 100 mA charging current in the battery charger display and still the capacity of the battery is very low.
I agree. Lead acid batteries can have reduced capacity and still "charge up" to the correct final voltage.

tpny

Joined May 6, 2012
216
i believe there's an internal resistance in the battery that gets bigger over time (from whatever reasons). (Observe the laptop battery..) So the total current capacity decreases over time even though voltage reads 12.7 or 13 or whatever it is u charge it up to..

kevinmaloe

Joined Oct 31, 2012
4
The value of the load current integrated over time will give you the battery Ah capacity.

tmd_63

Joined Oct 20, 2008
13
I would be a little concerned if your charger is measuring the voltage at 12.7V. A fully charged lead/acid 12V battery has a charged terminal voltage of between 13.2V and 14.4V. I have charged a battery with a constant voltage source of 13.8V and obtained a good lifetime cycle. But the only real way of checking the capacity is the C/10 discharge method. So, connect a constant current load at 720mA and see if it lasts for 10 hours.

MrChips

Joined Oct 2, 2009
20,904
Two ways you can damage a SLAB:

1) allowing the battery to remain below 12V for an extended length of time
2) not charging the battery fully

Charging the battery to 12.7V is not high enough. The battery must be charged to about 14.5V followed by a topping charge. You need to get a better charger.

This is the gold standard for battery information:

Battery University

crutschow

Joined Mar 14, 2008
24,735
Since your fully charged voltage seems low I would suspect a bad cell. What is the battery voltage under a small load?