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.

TEST RESULTS

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

And here are the results in a graph

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.

Conclusions

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.