zds – random thoughts

As the name implies, Low Self-Discharge NiMH batteries differ from their regular counterparts on retaining their charge for longer than the regular variety. These are especially useful for hobbyist photographers, because you don’t use your camera daily, but when you pick it up, you want it to work right here, right now.

To figure which of them I should buy in the long run, I have measured their effective capacity over different spans of storage time between full recharge and discharge.
The project is still on-going, but current results are presented on this page.

Contenders

Number of units tested in parenthesis. Results are reported as average of all tested units. Rated capacity is listed as printed to the unit itself.
Ansmann maxE, 2500mAh (4 units)
Maha Imedion, 2100mAh (2 units)
GP ReCyKo, 2050mAh (2 units)
Sanyo Eneloop, 2000mAh (2 units)
Sony CycleEnergy, 2100mAh (4 units)
Varta Ready2Use, 2300mAh (2 units)
Sanyo Eneloop XX, 2500mAh (4 units)

All units were straight from package, except Sanyo Eneloop and Varta Ready2Use, which had been used couple of times; not very long, but still not straight from package.

Methodology

Tests are conducted using Maha/Powerex MH-C9000 Charger-Analyzer. I do not have equipment to double-check the validity of it’s results, but this is one of the highest regarded piece of consumer AA/AAA analyzer and the results at least seem to be consistent, so we’ll base on that.

Before the actual tests started, I ran each of the battery units through the MH-C9000 “Break-In” program until the measured capacity did not change anymore. “Not changing” was determined by either results being closer than 1% of the previous run or trend being downward.

The “Break-In” consists of recharging the battery unit 16 hours at 0.1C (ie. 250mA for 2500mAh battery) and then discharging it fully at 0.2C (500mA for 2500mA battery) and then recharging again for 16h. This is also the IEC standard for determining battery capacity.

Before each run battery is charged to full at 1000mA, let stay stored at room temperature (approximately 25C) and finally discharged at 200mA after the given amount of days. These values were chosen to reflect the normal usage of DSLR camera owner; occasional conditioning for batteries, but most charges are fast. 200mA was picked by estimate to be somewhere between DSLR and compact camera usage.

Because of the obviously long waiting times included, this is still a work in progress. Storage times tested are 0, 14, 28 and 56 days (0, 2, 4 and 8 weeks). The results this far as graph:

(2011-06-08)

Keep in mind that the Y axis is truncated; most of these units would deliver practically the same amount of power at 4 weeks. The most interesting part is to look at the trends – for example Sony CycleEnergy starts higher than the rest (except Ansmann) but after 4 weeks it’s already in the bottom 3 of the bunch.

The Eneloop XX wins over everyone else, with Ansmann eMax trailing it by small but clear margin. After 4 weeks these two deliver more power than most of the rest straight from charger. After 8 weeks lead of Ansmann has dropped to 10% over the main pack, but it still carries more capacity at 8 weeks than the anyone else at 2 weeks, except Eneloop XX where we don’t have 8 week data yet.

On the loser side, Varta is declining fast. One of the two test cells posted alarmingly low numbers, 1290mAh after 8 weeks of storage. I am not yet sure if this is some anomaly, but I wanted to keep the field level by treating everyone equally, so I did not yet do any re-runs. More test units would solve the problem, so if someone wants to sponsor me those, I am happy to run them through the same tests. Out of Imedion, CycleEnergy and Eneloop CycleEnergy starts highest and Eneloop lowest, but after 4 weeks they are pretty much even, and remain so at 8 weeks, too.

To summarize: if 4 weeks is your typical storage time between charge and discharge, you can pick any of the brands listed here and not notice any difference, except Eneloop XX and possibly the Ansmann. Sanyo Eneloop XX delivers 24% and Ansmann eMax 15% more effective charge after 4 weeks of storage than the weakest of the contenders, Eneloop basic, which can make some difference.

Prices of the tested cells, set of 4, retail in Finland, May 2011:
GP ReCyKo: 17.16€ (Partco.fi)
Sanyo Eneloop: 17.90€ (Verkkokauppa.com)
Ansmann maxE: 17.96€ (Partco.fi)
Varta Ready2Use: 18,95€ (Clasohlson.fi)
Sanyo Eneloop XX: 24.90€ (Verkkokauppa.com)
Sony CycleEnergy Blue: 12.90€ (Verkkokauppa.com)

With these prices I see very little reason to buy basic Eneloops. Varta can fill a niché where you don’t need to store the batteries more than few weeks, but considering you can also get higher capacity non-LSD models for the same purpose at the same price range, that niché is really small. So with this data Eneloop XX takes hi-end crown, Ansmann eMax comes very close at lower price and Sony CycleEnergy Blue offers best value. Beware: Sony sells both LSD and non-LSD batteries with name “CycleEnergy”. Non-LSD ones are CycleEnergy Green, LSD are CycleEnergy Blue and read “Ready to Use”.

Yet another view is when we look at prices for non-Finnish (but still European) shops that talk English and deliver to Finland. Obviously you then need to figure in the cost of S/H.
Sanyo Eneloop: 8.99€ (Akkushop.de)
Sanyo Eneloop XX: 13.85€ (Akkushop.de)
Ansmann maxE: 15.95€ (Akkushop.de)

At these prices it’s hard to beat the basic Eneloop. So as usual, the value all depends on the price.

Note: While I report the source of prices, this roundup is financed by me personally and I do not have sponsorship or ties to any of the companies listed.

UPDATE 2011-07-21:
All models have now 56 day (8 week) results in. Eneloop XXs continue to dominate, offering some 22% more capacity after 8 weeks than basic Eneloops and more capacity after 8 weeks than most units straight from charger.

UPDATE 2 2011-07-21:
My friend noticed that Sanyo lists Eneloop XXs having lifetime of 500 recharge cycles, while basic Eneloops last 1500: http://us.sanyo.com/Battery-Products/XX-AA-4-Pack

Most of us don’t really get 500 recharges on our batteries during their lifetime (3-5 years), but something to keep in mind.

UPDATE 3 2011-07-21:
It would seem environmental footprint of NiMH cells is lower than Alkaline batteries after about 30-40 recharge/discharge cycles: http://www.springerlink.com/content/r104g3640u736674/

UPDATE 4 2011-09-03:
First 16 week (~4 months) results are in. The bad Varta unit keeps falling, and here the small sample size (just 2 units) really hurts the final score. However, with the performance even the better unit showing I’m not motivated to throw more money into getting more units.

For ReCyKo:s it’s a smooth ride; Sanyo CEO has commented Eneloops having inverse S curve on capacity retention, ie. after initial loss there is long plateau of very small drop until the charge starts to drop fast again. And GP ReCyKo:s seem to work exactly like that, too.