Hi everyone,
I had recently received a lot of SLA batteries. A bunch of 12V 7Ah Portalac APC batteries, which seems to be in good condition after testing. Also I had received three 6V 12AH batteries. A Fiamm-GS(it's kinda dead), but the other two CSB batteries seems to charge. But the issue is that after full charge and keeping it for a few days the battery voltage settles down to 6.33V and 6.35V for two batteries and then pretty much stays like that for quite a while. And it doesn't discharge either too quick when connected to a load.

So is the battery still okay? The date code as shown in picture says 991109M2. I'm not sure if it means 1992 & 2011.

 

Connect one 6V battery to a 6V lamp and measure the amount of ampere-hours you get before the voltage drops to 5.25V.

For example, a 6V/40W lamp will draw about 7A.
If the battery voltage drops to 5.25V after 1 hour, then the battery capacity is 7A x 1h = 7Ah.

If it lasts for 1.5 hours, then the capacity is about 7A x 1.5h = 10Ah

 

But make sure you take the load off before the volts go below 5.25V.
Running them to low volts will kill them.

 

Connect one 6V battery to a 6V lamp and measure the amount of ampere-hours you get before the voltage drops to 5.25V.

For example, a 6V/40W lamp will draw about 7A.
If the battery voltage drops to 5.25V after 1 hour, then the battery capacity is 7A x 1h = 7Ah.

If it lasts for 1.5 hours, then the capacity is about 7A x 1.5h = 10Ah

Thanks mate. I'll try this and report the results. I've a question. I'm planning to use two GE 4510 6.4V 25W in parallel as load for testing above method. So my current draw should be around 7.9A.

So while measuring the capacity you did mention I've to make sure the voltage doesn't drop below 5.25V right.

So, when the load is connected the voltage should drop. Did u mean the voltage (5.25V here) when connected to load or 5.25V after the load is removed? Because the voltage does rise after load removal.

 

The measured capacity of a battery will change with the discharge current.
Discharging a battery at 1C, for example, discharging a 12Ah battery at 12A is a bit strenuous on the battery.
Discharging at C/10 or C/20 is more forgiving on the battery.

I used a 6V/40W bulb as an example which is my error. I should have suggested something lower such as 6V/5W.

Instead of using two 6V/25W bulbs in parallel, put them in series to give a lower current draw.

The voltage should not drop below 6V on immediately connecting the load. You are looking for the time it takes for the voltage to drop to 5.25V. The fact that the voltage rises after removal of the load has no bearing on this test (except for the fact that it indicates that the internal resistance is on the rise which means that the battery is due for retirement).

If you can get a few of hours service with the two 6V/25W in series as a load then there is still some useful life left in the battery (depending on where you plan to use this battery).

 

Hi,

Yeah the normal test is C/20 which is the ampere hour rating divided by 20 hours.
So for a 10 ampere hour battery the load should be 10/20 or 1/2 ampere.
For a 5 ampere hour battery the load should be 5/20 which is 1/4 ampere.

Yeah it takes longer to test that way but that's the standard

For the 1 hour test i think the ampere hour capacity is roughly halved, so a 10 ampere hour LA battery would measure about 5 ampere hours, but it's dependent on the internal resistance too so it can vary a bit.