Hi, I’m Rob, and I’m a hoarder collector
I have a lot of batteries.
Sealed lead acid, AGM, Gel, Lipo, Li-ion
The things they all have in common:
Needed to keep things running
Not cheap
Harder to test
They don’t come with a gas gauge (usually)
Batteries are rated in mAh, of Ah and voltage. For the sake of this post, we’ll be dealing with only 12v batteries, like a car battery, but not.
Formula is (mAh)*(V)/1000 = (Wh). For example, if you have a 300mAh battery rated at 5V, the power is 300mAh * 5V / 1000 = 1.5Wh.
In TODAY’S case:
I have a 26000mAh battery rated at 12V, the power is 26000mAh * 12V / 1000 = 312Wh.
But how does one tell if its ACTUALLY 312Wh, or 31 Wh?
My testing process:
*disclaimer*
MY testing process will just be “good enough” I don’t work for NASA building things that go into space. I just need to be “close”
Step 1: Charge the battery till complete with my CTEK 25000 12V 25Amp Battery Charger
This process allows me to remove the bottom of the barrel packs right away – If the CTEK can’t charge it, it goes to the recycle pile, quick and easy. If the get the green light from the CTEK, we move on to step 2
Step2: Build a load.
For my load, I’m using a 400 watt inexpensive 120v power converter. I’m looking to waste as much power as I can, so it doesn’t need to be pretty. Today, I have a pair of lights plugged into the inverter. This load is about 12v @ 6amp, which seems to work pretty well..
Now, the gas gauge for this project: Power Analyzer
The link isn’t exactly the same model, I have several, and they all seem to work about the same, and look the same.
Step3: Test.
I connect the meter to the battery (source)
Connect the inverter load to (load)
Turn on the inverter power switch.
Wait.
You’ll have to excuse the scribble that is my handwriting, but the key part is to note the results on the pack
As you can see, the first 3 packs differ greatly.
Glad I only have 10 to do, these can take from 2 mins, all the way to an hour each.
| Battery # | AmpHour | WattHour | Rated Wh | % of Capacity |
| 1 | 0.00 | 0.00 | 312 | 0.00% |
| 2 | 0.00 | 0.00 | 312 | 0.00% |
| 9 | 0.00 | 0.00 | 312 | 0.00% |
| 3 | 0.50 | 4.90 | 312 | 1.57% |
| 4 | 1.12 | 13.38 | 312 | 4.29% |
| 5 | 3.90 | 47.00 | 312 | 15.06% |
| 6 | 4.94 | 59.30 | 312 | 19.01% |
| 10 | 6.27 | 68.60 | 312 | 21.99% |
| 7 | 19.16 | 210.00 | 312 | 67.31% |
| 8 | 19.40 | 232.00 | 312 | 74.36% |
Step4: Remove the known bads, recharge the possible goods
Back to the CTEK 25000
Step5: Retest
Step6: Determine a threshold
I’m choosing 65%, but we’ll see.