Moixa Energy USBCell AA batteries are practical for an on-the-go gadget addict. These attractive, compact batteries resemble other nickel metal hydride AAs, except for a bright green cap covering the USB plug. Instead of tossing them in the trash or nestling them into a recharging unit when out of juice, you can pop these into a USB port on any laptop or other USB device.

Design
The USBCell design is excellent and feels sturdy. When opened, the cap reveals a pair of tensile cords attaching it to the battery. We pulled and pulled, but couldn't break them.

The batteries' LEDs light up around the base while inside a USB port, and flash slowly some 20 minutes later when the battery warms up to a 90 percent charge. The light turns off when the AAs are ready for use.

Unfortunately, depending on how close your USB ports are to each other, you might not be able to plug in two or more USBCell batteries side by side at the same time. That's a major flaw, perhaps, if your laptop only features two side-by-side USB ports and you lack a third-party recharging kit.

Features and performance
USBCell AAs can replace comparable batteries altogether, especially if you have USB ports at the ready. But we wouldn't throw away standard batteries. Instead, we found it useful to carry both the USBCell batteries in addition to a pack of rechargeable NiMHs.

Luckily, USBCells also fit into standard AA battery chargers. That could take up to 7 hours to recharge in a 250-milliamp charger. The vendor doesn't recommend 2-hour, 600-milliamp chargers.

Our rechargeable Duracell NiMH AAs were rated to store 2,300-milliamp hours, eclipsing the 1,300-milliamp hours of the USBCell equivalent. We found that a pair of fully charged USBCells lasted in a Canon point-and-shoot camera after shooting close to 600 pictures, while the Duracells lasted for more than 1,000 shots. In a small Flip video camera, the USBCells lasted for several hours of footage before needing more juice (we didn't measure the life of the other AAs in this device for contrast). USBCell batteries are meant to last 500 cycles, or several hundred charges.

USBCell batteries can be recycled along with other NiMH batteries. Their packaging earns "green" points for recycled cardstock printed with vegetable inks.