With rechargeable batteries, you have to make a tradeoff between power and service life. High-power batteries, which can store over 2,400 mAh of charge, last longer both in your devices and on the shelf. However, they can't be discharged and recharged as many times as lower-powered batteries that hold just 2,000 mAh. So the best battery for you is one that delivers as much power as you need, but no more.
For most users, we think the 2,300 mAh Energizer Recharge Power Plus ($17 for 8 AA batteries) strikes the best balance between power and longevity. In TheWirecutter.com's tests of AA rechargeable batteries, this NiMH battery is the top pick, with high scores for both capacity and real-world run time. TheWirecutter.com also reports that these batteries hold their charge well and that they were still going strong in a wireless mouse and keyboard after 6 months of steady use.
Electronics enthusiast Stefan Vorkoetter, writing at his site, StefanV.com, has conducted extensive comparison tests of rechargeable batteries and confirms that the Energizer Recharge Power Plus batteries have a high capacity when freshly charged and hold over 85 percent of that charge after seven weeks in storage. Energizer claims that these batteries can be recharged "hundreds of times" and have a lifespan of up to five years with typical use. In addition, they're guaranteed to hold their charge for up to 12 months in storage. Reviewers at Amazon generally confirm that these batteries have a long service life and hold a charge well. However, some say they don't last that long in high-drain devices, such as camera flashes.
Energizer Recharge Power Plus batteries are available only in sizes AA and AAA. However, Energizer also makes the Energizer Recharge (Est. $10 for 2 C batteries) NiMH battery, which comes in C, D, and 9-volt sizes. These batteries can hold a charge just as long as the Recharge Power Plus, and Energizer claims they can be recharged up to 1,000 times. According to Energizer, this gives the larger-sized batteries a total lifespan of up to 3 years with normal use.
One drawback of these Energizer batteries is that they don't come pre-charged. You have to charge them up before their first use, and tests at Engadget find that they take longer to charge than most other rechargeable batteries. If you want to be able to take your batteries straight out of the package and use them immediately, a good alternative is the 2,400-mAh Powerex Imedion (Est. $25 for 8 AA batteries). At Michael Bluejay's Battery Guide, energy expert Michael Bluejay names this as his favorite NiMH rechargeable battery because of its high capacity and low self-discharge rate. Every source we've consulted says the Powerex Imedion holds its charge very well, keeping anywhere from 65 percent to 85 percent after a year in storage.
Most reviews also say the Imedion gives you plenty of power on a charge. In TheWirecutter.com's tests, the AA battery performs about the same as the Energizer Recharge Power Plus. The only reason it doesn't take the top prize is that it's a little pricier than the Energizer and a bit harder to find in stores. A second professional test finds that the Imedion runs longer on a full charge than almost any other brand.
When it comes to overall life span, however, the Imedion is less impressive. In one professional test, Imedion batteries don't make it through the full 200 rounds of charging and draining, dying after fewer than 100 cycles. Several users at Amazon also report that the Imedion's capacity starts to drop off sharply after 10 recharging cycles or even fewer. Another problem some reviewers note with the Imedion is that the AA battery doesn't fit in some devices.
Between this and the longevity problem, the Imedion is not as good a choice as the Energizer Recharge Power Plus for users who specifically need rechargeable AA batteries or rechargeable AAA batteries. If you need a C, D or 9-volt battery, however, Imedion is probably your best choice. The C and D cell Imedion batteries hold twice the charge of similarly sized Energizer Recharge batteries. So for large devices that use several C or D batteries, choosing the Imedion means you won't have to recharge your batteries as often. Imedion also makes two 9-volt equivalents, one with 230 mAh and one with 250 mAh charge capacity – both significantly more than the 175-mAh Energizer Recharge.
If you only need rechargeable batteries in AA and AAA sizes, it's worth looking at the popular Panasonic Eneloop Rechargeable ($20 for 8 AA batteries) or Panasonic Eneloop Pro (Est. $35 for 8 AA batteries). The Eneloop Rechargeable has a lower capacity than other NiMH batteries, just 2,000 mAh. That means it peters out faster than other rechargeable batteries, particularly in high-drain devices. However, these batteries make up for their lower power with an exceedingly long service life. According to Panasonic, the latest generation of Eneloops can be recharged up to 2,100 times. No one has ever tested this claim fully, but the batteries make it handily through 200 charging cycles in one professional test with no discernible drop in charge capacity.
The other advantage of the Eneloop Rechargeable is its very long shelf life. Panasonic claims that Eneloops retain 70 percent of their charge after ten years in storage. While no one has tested the batteries over this long a period, several reviewers at Amazon.com have found their batteries still hold a charge after as long as five years on the shelf. Much of the drop in power seems to take place over the first few weeks; Vorkoetter found that Eneloop batteries dropped to less than 90 percent of their charge after seven weeks.
The Eneloop Pro, by contrast, has an unusually high capacity of 2,550 mAh, allowing it to power devices longer between charges. In the one test that includes both Eneloop and Eneloop Pro batteries, the Eneloop Pro lasts an average of 118 minutes on a charge, while the regular Eneloop lasts only 92 minutes. Moreover, Amazon users say these batteries perform better than any other brand in high-drain devices. Several photographers say their flash bulbs recharge noticeably faster when they're using Eneloop Pro batteries.
However, Eneloop Pro batteries don't have nearly as long a lifespan as the regular Eneloops. Panasonic says they can be recharged up to 500 times, but professional tests say otherwise. In one test, the batteries are still going strong after 60 recharges, but they fail before making it to 100. Another downside of the AA Eneloop Pro is that it's slightly wider in diameter than a standard AA battery, so it won't fit into all devices.
The bottom line is that if you need an AA or AAA battery with the highest possible capacity, and you're willing to pay for it, the Eneloop Pro is a good bet. On the other hand, if you don't need that much power and you want your batteries to serve you for many years, the Eneloop Rechargeable is the best choice. And if you want a middle ground, combining decent power with a decent service life, stick with the Energizer Recharge Power Plus.