Following september mourn: how much confidence do you have in advertised battery capacity?

[rin67630]

I have now measured the solar Lead-Acid "100Hh" battery capacity that I recently bought:
Here are the figures of a discharge at roughly C/200 during bad weather conditions, followed by a charge, assisted by a regulated power supply.
The discharge stopped at 11,5V, the charge at 14,2V.

ts	AhBat[26]	voltageAt23:59h
2020-09-25T22:00:01.767Z	0.14​	12.69​
2020-09-26T22:00:01.755Z	-5.86​	12.59​
2020-09-27T22:00:01.513Z	-4.11​	12.47​
2020-09-28T22:00:01.526Z	-8.45​	12.41​
2020-09-29T22:00:00.792Z	-9.56​	12.26​
2020-09-30T22:00:01.818Z	-1.31​	12.07​
2020-10-01T22:00:01.151Z	-7.11​	12.04​
2020-10-02T22:00:01.873Z	-4.15​	11.87​
2020-10-03T22:00:01.443Z	-9.20​	11.77​
Discharge	-49.62​	Ah
2020-10-04T22:00:00.469Z	8.52​	11.74​
2020-10-05T22:00:00.906Z	4.17​	12.04​
2020-10-06T22:00:00.950Z	15.84​	13.06​
2020-10-07T22:00:01.716Z	26.38​	14.08​
Charge	54.91​	Ah

I would consider having got a 50Ah battery at its most. 50% of the sold performance, under very favourable conditions!

Is that the standard cheating of the industry?
What is your experience on advertised/real capacities?
The battery weighs 18Kg. Is that compatible with a 100Ah solar battery?
I thought solar batteries are more massive than cranking ones.

The vendor has agreed to replace it, but what if i get the same crap again?

Thank you for your advice.
Laszlo

 

[Ampster]

Did you use a meter that calculates Ahrs? The usual range of voltage that the cells are rated at is from 3.65 to 2.5 volts per cell. I would run another test going to the full voltage settings. It looks like your test only went to 3.52 volts per cell (14.08÷4)

 

[rin67630]

Did you use a meter that calculates Ahrs? The usual range of voltage that the cells are rated at is from 3.65 to 2.5 volts per cell.

I forgot to mention that I was speaking of lead-acid batteries.
Yes my self-built battery monitor integrates the battery current every second and calculates Ah by the minute, hour, day...

 

[Ampster]

Sorry, forgot most of what I ever knew about Pb. They only have 50% usable anyway and need absorbtion charge which makes them inefficient.

 

[Sabre36]

To properly capacity test a lead acid battery it is discharged at the 20 hour rate with the current held as steady as possible. For a 100AH lead acid battery this is 5A. The battery must also be at or close to 77F and discharged to 10.5V where you stop the discharge and record the discharge time or read the Coulomb counter and then immediately recharge. Recharing does not stop at 14.2V it must continue at the recommended absorption voltage until the accepted current has dropped below 1% of rated Ah capacity or lower. Most AGM's specify a tail current of 0.5% or 0.3% at absorption voltage. If you stopped charging when the battery hit 14.2V you may have only been at 75-80% SoC. Lead acid requires a long absorption duration.

Lead acid batteries also take time to "cycle up" to their rating so a brand new battery will rarely if ever deliver 100% of its rating. That said flooded auto type lead acid batteries (G-24, 27, 31 4D and 8D) are often quite a bit off their rating where as a deep-cycle product such as a GC2, L-16 etc. generally do deliver their ratings.

 

[rin67630]

To properly capacity test a lead acid battery it is discharged at the 20 hour rate with the current held as steady as possible. For a 100AH lead acid battery this is 5A. The battery must also be at or close to 77F and discharged to 10.5V where you stop the discharge and record the discharge time or read the Coulomb counter and then immediately recharge. Recharing does not stop at 14.2V it must continue at the recommended absorption voltage until the accepted current has dropped below 1% of rated Ah capacity or lower. Most AGM's specify a tail current of 0.5% or 0.3% at absorption voltage. If you stopped charging when the battery hit 14.2V you may have only been at 75-80% SoC. Lead acid requires a long absorption duration.

Lead acid batteries also take time to "cycle up" to their rating so a brand new battery will rarely if ever deliver 100% of its rating. That said flooded auto type lead acid batteries (G-24, 27, 31 4D and 8D) are often quite a bit off their rating where as a deep-cycle product such as a GC2, L-16 etc. generally do deliver their ratings.

Thank you for that insights.

My battery was at absorption at 14,4V 20 days before discharging (every day for about 4 hours). It discharged due to bad wather on a load of ~500mA only and the regulator did cut the discharge at 11,5V.
I got less than 50Ah out of that discharge cycle.
Is that acceptable?
(The battery has enough fluid level, I checked that !)

I suppose that I could have got 5-6 Ah more until a deeper discharge of 10,5 V, probably not very much more, right?
On the other side, I was far under C/100 and hence should have even got more Ah than rated, isn't it?

Anyhow the vendor agreed to replace the battery against a proof of dumping mine properly at an official recycling yard.

But are the batteries usually sold generally that much overrated?

 

[Ampster]

I got less than 50Ah out of that discharge cycle.
Is that acceptable?

Sorry for the shameless plug for Lithium batteries but it was not acceptable to me on an ebike project 10 years ago. That is when I switched to Lithium. I even converted a NiCad powertool pack to Lithium with some smokey results.

 

[rin67630]

Sorry for the shameless plug for Lithium batteries but it was not acceptable to me on an ebike project 10 years ago. That is when I switched to Lithium. I even converted a NiCad powertool pack to Lithium with some smokey results.

Lithium is a bit too touchy for me, I have ruined dozens of 18360 batteries on a single deep discharge, and my outdoor project cannot prevent temperatures below 0°C.
Weight is an advantage for me.