As long as I had the battery life test circuit wired up, I decided to test as many kinds as I could. Each test takes from half a day to a day, tying up my development system while running. The tests could have been done with greater rigor, but as this is just a little side trip, I’m willing to commit to neither the time nor the expense of larger sample sizes and better controls.
Here are the results. The chart will be updated as more batteries are tested. Don’t see your brand on here? I’m open to suggestions!
click on graph to display full size
Details on the batteries tested follow. The full OpenOffice Calc spreadsheet is linked near the bottom of this article.
These Tenergy AAA batteries were about $1 online. None of these prices include tax or shipping, of course. It was able to supply 100 mA for 7.42 hours, so the capacity was judged to be 742 mAh.These Yuasa batteries were so generic, the manufacturer’s name was in fine print. I picked up a bunch of these used at a flea market for 25¢ each, from someone who had 5-gallon bucket of them. Test result 1473 mAh – not bad for a 25¢ rechargable.At Costco, I got the second to the last package of these Eneloop (Sanyo) 1900 mAh batteries. There wasn’t even a price card on the rack for these older models. The newer version of these batteries has raised the stay-charged time from 3 years to 5 years, and now claims 1800x rechargeability. It was $14.95 for the pack of 10, making these $1.50 a piece. The package claims the cells are ready to use, so I tested one right out of the package without charging, then tested another cell after a full charge. After charging, the Eneloop had as much capacity as a name-brand Alkaline, at a lower price point. Even if this rechargeable was immediately discarded after one use, it would still be more cost-effective. Test result 1962 mAh – more than the label rating.These three alkalines were lying around in a drawer. The Energizer (Eveready) was date stamped for 2012, so was 2 years past fresh when tested. The Duracell said March 2012, so was also 2 years past fresh. The Kirkland (Costco) cell was marked 2013, one year past fresh. I don’t remember how much these cost, but the Kirkland was probably much cheaper than the other two. The Kirkland also significantly underperformed, but since all of these batteries were just lying around, it could be that the Kirkland one was partially used, already.I got these new at a flea market for $1.50 each, several years ago. The button on the end has slightly unusual dimensions, so this doesn’t fit in all devices. This battery will put out 9A of short circuit current, although it performed poorly on my test setup. Perhaps it’s made for very high drain applications.I believe I got these for $1.50 each also at a flea market. Test result 658 mAh.I found 4 packs of these Lithium-Iron non-rechargeable cells at a flea market at 2 packs for a dollar. That’s 12.5¢ each. The life was amazing (2690 mAh); I’ll snap up more of these if I see them.Just for fun, I picked up an 8-pack of regular carbon-zinc batteries from Dollar Tree. That works out to 12.5¢ each. If we are counting only the length of time that the battery can put out 100 mA, we get 1048 mAh as the capacity – not bad for the price. But unlike the other battery chemistries, the voltage on carbon-zinc sags quickly, making the usable capacity more like 720 mAh. For use in a low drain application like a clock, why not? They’re cheap. The “Best By” date was 31 months in the future when one of these was tested.As long as I was at Dollar Tree, I also got a 4-pack of Alkalines for $1. That’s 25¢ each. Note the expiration date, 6 years in the future at the time of test. One of these tested out at 2150 mAh, with a practical life of perhaps 2000 mAh. This was superior to the best NiMH tested, suggesting that even a cheap Alkaline battery is on par with rechargeables, if the Alkaline is fresh.These are the AA cells mentioned in a previous post. They have the highest label capacity, and the lowest actual capacity – inferior even to the AAA batteries tested.I got these Energizer e2 Lithium batteries for $1 each at a flea market perhaps 5 years ago. They have an expiration of 2019 stamped on them, 5 years into the future from the test date. This one tested out at 1983 mAh of capacity, of which about 1870 mAh was useful. One thing about getting things at a flea market, they could have been used. Possibly these batteries were used in professional microphones, then swapped out long before they were dead. The Powerizer Lithium-Iron batteries were outstanding, but then again, they came in sealed packages.I got these from eBay about 15 (yes, fifteen) years ago, for about $2.50 a piece. At the time, NiMH consumer batteries were just starting to displace NiCd. These generic cells have no markings other than “EFH Japan,” but the eBay listing said that they were 1600 mAh. My test setup read 1375 mAh, very respectable for batteries that have been in continual use for 15 years. But get this: the usable capacity was 1370 mAh. That is, this cell kept on putting out 100 mA at 1.0 volt until almost literally the last minute.I picked up four of these Tenergy NiMH D-cells from the internet, for $8 a piece. This one turned out to have about 7500 mAh of capacity, 7000 mAh usable. The timescale for a D cell is so much longer, I made a separate graph below, against some selected other cells.
