AA Battery testing

This is simply about how I tested a bunch of old AA rechargeables.

As it is quite possible we may get some power cuts this winter I decided I may want to make use of some old batteries we have. It actually adds up to quite a bit of energy storage.

Before retirement I was a professional photographer, and I did a lot of weddings and events.  I used a Nikon SB800 flash units which take either 4 or 5 AA batteries.  After some trial and error I settled on Panasonic Eneloop batteries.  These hold their charge for a really long time in between charges, so after a shoot, I could recharge the batteries, and they were ready for the next time.  I always carried a spare set as I could take a lot of pictures at some weddings and the batteries simply ran out.  It was good to know the spare set were good to go even though the last charge could have been months before.  That was a long time ago, so all of my batteries are quite old. I found information about the batteries on line at eneloop101.com.  I have also acquired a few other batteries, a few “Energisers, some “Tronix” and some non eneloop Panasonics.

All of my AA’s are Panasonic and most are first Generation, which came out in November 2005. The second generation came out in 2009, so most of my batteries are between 13 and 17 years old.  Some are third generation which were produced between 2011 and 2013. So these will be 9 to 11 years old.  As regards the the other batteries, I have no idea of the age.

I decided to check them out.  On a bank of batteries in series, the capacity is only as high as the lowest capacity battery. 

I  used my old home made battery checker (left). This comprises an old battery clock with a bulb connected across the battery terminals. (The dymo taped numbers on the clock are from when I was teaching my son how to read an analogue clock – around 35 years ago!)  The clock is set to 12:00 and the battery inserted.  The battery powers the bulb until the voltage falls too low to power the clock and it stops. The time on the clock records that time.  The bulb takes around 0.58A.
NiMH batteries have a quite sudden drop off as they run out of power so this is a reasonable estimate of the capacity. Also, when 10 batteries are connected in series to power a 6W led bulb (or a 7.5W Busking Amp) the current taken is of this order A so the time measured will be around the same time that the bank will last before a recharge.

According to eneloop101 new batteries have a capacity of around 1800mAh (this is actually measured) so new batteries would last around 3 hours on the tester.

First the batteries were charged, 8 at a time on my old charger (everything is old with me!)

Then they were numbered and put on the tester one at a time.  The time until the clock stopped was recorded for each battery. The charger will sometimes refuse to charge a particular battery.  I do not know the algorithm it uses to decide.  I have found that sometimes a kickstart helps

Kickstart flat AAs.

Using a power supply to force some current into a battery will put it into a state that the charger will accept.  I tried with 250mA for 1.5 hours with some batteries and 3 non-eneloop Panasonic and 1 Energiser did not respond.  One eneloop and 3 Energisers did respond. 

Once they responded I could fully charge them on my V8 supercharger.


None of the Tronix batteries lasted more than 10 minutes in the tester so are not recorded.

Current in Amps =0.58  
Battery NumberDischarge timemAHBattery Code
100:22:45220Panasonic HR-3UTG
202:42:371572Panasonic HR-3UTGB
301:56:001121Panasonic HR-3UTG
401:40:00967Panasonic HR-3UTG
502:26:001411Panasonic HR-3UTG
601:37:00938Panasonic HR-3UTG
701:56:001121Panasonic HR-3UTG
801:24:00812Panasonic HR-3UTG
902:34:001489Panasonic HR-3UTGB
1001:26:00831Panasonic HR-3UTG
1102:35:001498Panasonic HR-3UTGB
1200:28:00271Panasonic HR-3UTG
1302:16:001315Panasonic HR-3UTG
1401:43:00996Panasonic HR-3UTG
1501:33:00899Panasonic HR-3UTG
1602:30:001450Panasonic HR-3UTGB
1702:29:001440Panasonic HR-3UTGB
1802:29:001440Panasonic HR-3UTGB
1902:30:001450Panasonic HR-3UTGB
2002:32:001469Panasonic HR-3UTGB
2101:49:001054Panasonic HR-3UTG
2200:31:00300Panasonic HR-3UTG
2300:31:00300Panasonic AA-p-6p

And here are the results in a graph

The highest 8 values ar all Eneloop 3rd generation. Then follows the recovered Energiser, then the Eneloop 1st Generation except No 23 which is a non Eneloop Panasonic

The Generalised Iceberg Theorem (90% of everything is beneath the surface) strikes again.

Eneloop batteries 1, 12, and 22 seemed to be fairly clapped out, lasting less than 30 minutes on the tester.  As a matter of course I put batteries back on the charger after the test.  So, out of interest, when I had tested all the batteries I ran the test again on Battery No 1. It managed 2 hours and 30 minutes!  That is 1450mAh from 220 on the first run

What is going on here?  Does a couple of charges revitalise the battery, or is it a charger issue? Battery No 1’s capacity has seemingly gone uo by a factor of over 6, and it’s now in the middle of the 3rd generation eneloops.

So, I did the same with 271mAh battery 12. It lasted 1:45 this time making it 1015mAh; still very respectable for a 15 year old battery.

300mAh Battery 22 improved to 822mAh, not as dramatic, but still more than doubling.

I decided to try it with an “average” 1st Geneneration so I chose battery 7.  It lasted 1:56 on the charger first time around which was pretty good.  This time it managed 2:30, once again taking it into the realm of the 3rd Generation batteries.

So I decided to re-test all of the low measuring 1st Gen batteries.

The group to the right are 3rd generation Panasonic Eneloops and those on the left are 1st generation


Panasonic Eneloops last a long time.  I have 8 ten year old batteries with a capacity of over 1400mAh. (they would have been around 1750mA when new).  These are 3rd generation eneloop (the latests ones are 5th generation).  The 1st generation seem to benefit very substantially from a few discharge and charge cycles.

 My 1st generation batteries, around 15 years old would still be serviceable in situations where around 1000mA is adequate. A bank of 10 will provide 6W for around 2 hours.

My old non-eneloop batteries, six cheap Tronix batteries (under 3 years old I think) are heading for the recycling centre.

Some older Energiser’s need a kick start to get then into a state that my charger will take over. Two others seemed to recover but could not provide enough voltage to drive the clock while powering the bulb.  As 3 out of 4 were not serviceable and I don’t have much that uses a single rechargeable battery I think I’ll avoid them.

This has proved to be a very worthwhile investigation. I started with the aim of having a reasonable capacity bank of 8 rechargeable batteries.  I have ended up with having two banks of 10 eneloop batteries, one with 1440mAh and one with 900mAh.

Anything other than Panasonic Eneloops is false economy.