The only USB-C AA battery I’d buy for myself is the Zepath 3600

It gave me an idea. Could we find the very best USB-C AA batteries by combining my own anecdotal testing with Lumafield’s scanning tech?

The answer seems to be yes! Knowing what I now know, the Zepath 3600mWh is the only rechargeable lithium-ion AA I’d buy for myself — even though USB-C is in the charger, rather than each individual cell.

$20

The Zepath is the only one that passed both Lumafield’s test and my test with flying colors. It has higher capacity than most of the competition, it’s easy to use, and incredibly, it’s one of the cheapest of its kind.

These AAs cost just $2.50 per cell, less than Panasonic’s famed Eneloop nickel-metal hydride (NiMH) batteries, all while lasting much longer than even Eneloop Pros in my Game Boy Advance and high-power flashlight.

It’s $20 for an eight-pack, and that includes a clamshell charger with a magnetic snap closure. (Think earbuds case, but much larger.) You can drop as many or as few batteries as you want into any of those eight slots — it’ll happily charge three dead batteries alongside three full ones, even if you arrange them in a zig-zag pattern. It pulls about 10 watts to charge all eight batteries at once, and under 3 watts for a pair. You can use either a dumb USB-A-to-USB-C cable or the same kind of USB-C PD charger you use for your phone or laptop.

Plus, the charger has built-in safety precautions that keep it from charging the wrong kinds of batteries. You’ll see eight hidden LEDs shine through the top of the case to indicate whether a battery’s charging (blinking green), charged (solid green), or rejected (blinking red) because you accidentally put an alkaline or NiMH inside instead.

Again, this means the only USB-C AA battery I recommend doesn’t have a built-in USB-C port — but I have good reasons for that.

When Lumafield analyzed 12 different kinds of lithium-ion AA batteries for The Verge, including designs with both built-in USB-C ports and ones with clamshell USB-C chargers, almost every battery other than Zepath was inferior.

Some, like Paleblue, had tried to cram a tiny pouch cell into the battery’s can to make room for the USB-C port. Others, like Coast, use a “can-within-a-can” design, where a smaller preexisting 14400 cell (14mm x 40mm) nests inside the larger battery.

Either way, Lumafield’s Alex Hao found most have relatively poor alignment and one had negative anode overhang, the same worrying defect she discovered in the earlier study of 1,000 larger cylindrical cells. Almost every “Good” we scanned was one with a charging case, including Philips and Mupoer. But the best were Zepath and the very similar Runpower — and Zepath costs less.

Scans of four different Zepath cells. “The additional Zepath batteries we scanned were consistent in their quality,” writes Hao.

“This battery has fairly straight alignment and even anode overhang (AOH). The assembly quality looks good. And the electrodes really maximize the space available in the can. Overall this is a good battery,” is how Hao described the Zepath scans.

I had high hopes for batteries from Coast and Nitecore, with their built-in USB-C ports and their brand reputation for building high-quality flashlights for very savvy clientele. (Costco carries the Coast batteries; this is not a fly-by-night brand.) But Hao thought Coast’s battery looked “a little wonky” with unusually low anode overhang. “There still is overhang, so this battery doesn’t seem super unsafe, but I wouldn’t choose it over others in this cohort,” she noted.

And while she didn’t think the Nitecore was dangerous, the company may have a quality-control issue: Both Hao and I noticed our batteries felt a bit loosely put together, with top terminals that weren’t always straight, and some of the cells Lumafield scanned had shorter overhangs and worse alignment than others, Hao said.

The batteries you might want to avoid are Spyong, which I see has already been pulled from Amazon since Lumafield discovered one cell was entirely deformed inside and had negative anode overhang; NTONPOWER, which had very poor electrode alignment according to Hao; CZVV, which had “virtually non-existent” anode overhang along the bottom of the cell and has also disappeared from Amazon, and surprisingly, Paleblue, a known brand where our internal pouch cell appeared to have anodes bending inward, which could lead to short-circuiting if they ever manage to touch.

By the time I got Hao’s results back, I didn’t mind giving up the USB-C port. I’d already discovered two practical downsides to built-in sockets.

The first: shorter battery life. The Zepath lasted an entire hour and a half longer than the Coast in my screen-modded Game Boy Advance at max brightness; they lasted two hours longer in my budget 1,000-lumen flashlight. (See some of the results in my embedded video above.) And when I tried two different sets of Nitecore in that Nebo flashlight, they strangely didn’t work at all, either turning the high-power LED into a flickering mess or refusing to stay on.

The second reason: This generation of integrated USB-C batteries is fiddly to plug and unplug. The sockets feel too tight on most of them, enough that I feel like I’m risking damage to the battery by forcing it in and out.

And though it might be annoying to remember to pack the Zepath charging case, it’s also possible to forget the four-headed USB-C charging cables that come with the integrated batteries. It’s nice to have an integrated port when you’re charging just one or two batteries, though.

Lithium-ion AAs are not the ultimate battery, port or no. The chemistry is still inherently flammable, even if these ones have a metal casing that protects them from repeated drops, and not all devices benefit from having batteries that reliably put out around 1.5 volts until they’re about to die.

My flashlight lasted a lot longer on low power with NiMH batteries, which die far more slowly, even if the Li-ion batteries worked better on high. So even though I’ve added some Zepath batteries to my home, I won’t be getting rid of Eneloops anytime soon.