The users over at reddit.com/r/AAMasterRace recently got some traffic from the Nanfu guys. Since I do some cell testing, I agreed to test these Nanfu Tenavolts. They’re AA sized lithium ion cells, which are bucked down to the more common 1.5V for AA NiMH or alkaline cells. The claims these make aren’t trivial, so I was interested to test them.

This isn’t a typical cell test, either. I’m mainly looking at work hours, and also to see if the claim that these hold 1.5V for the duration of their discharge is true.

As always, click for bigger images!!!

Official Specs

Here’s a referral link to the official product page. At least, that’s the link my contact gave me, and exactly from where I obtained these.

Price

$35 for four cells and a charger on amazon. That is an amazon referral link.

Short Review

These seem to meet their claim. Whether they’ll be useful to you with your current setup is a different matter entirely. But the mWh and voltage claims do seem to be accurate.

Long Review

Package

Fancy printed box.

The goodies are in a plastic tray.

What’s Included

Tenavolt 1.5V AA sized cells (4)

Tenavolt charger, 4-bay

Manual

Charge cable (USB to micro-USB)

Build Quality

No complaints on the cell build quality. For whatever reason I found it hard to distinguish positive from negative end, despite it being exactly like all other cells. I think it has to do with the wrapper – I kept expecting the light blue end to be the positive end.

This charger is only for Tenavolts. It is not to be used for any other type of cell. Not NiMH. Not 14500 Liion cells. Only Tenavolts.

The included charger will fit AA or AAA sized cells.

The bays are conveniently imprinted with the correct cell orientation.

The charger has a cover, too. I found the cover to be fiddly, and while there is a relief for easy access and removal, I just stopped using it entirely, and went topless.

Below, the positive terminal.

Below, the negative terminal.

Here’s the charge cable.

Size

Officially 50.5mm x 14.5mm. It’s AA sized, or maybe just shorter.

Testing

This is a complete one-off test, so nothing else on the site will compare. So scales don’t matter too much. Also I haven’t performed the full array of tests – no temp for example. And no full charge test, since the charge must be done in the provided charger (though, I could probably replicate it on my tester now that I’ve seen it. It’s unusual charging (see below).

Discharge tests

There are a few things to notice here. First is that the cell absolutely holds 1.5V flat for the duration of the output. Below is just a blowup of the above X axis. I was a little surprised how similarly the cells performed. I was testing 8 cells, and began testing straight off their charger.

Capacity

Energy

Here’s the most important test. Nanfu only makes a claim on Wh instead of the more common (but honestly probably less useful) mAh.

At 0.2A, the Tenavolts hit their claimed mWh of 2775.

There’s some interesting math going on here that could potentially be a good lesson in energy. It starts with a teardown of these cells (which I didn’t do, but you can find videos of easily. I could even link one.) Inside this AA sized cell is a lipo pouch cell (!!!) of 750mAh. But wait, you say, how’s this 750mAh?? It’s all in the buck. That 750mAh cell is at 4.2V, but these output only 1.5V. So what we should consider is Wh. And the cell even has it listed – 2.78Wh.

750mAh @ 3.7V (that’s nominal voltage of a Li-ion)= 2775mWh

Bounce

“Bounce back” is what the cell voltage does when the cell rests after a discharge. After heavy discharge rates, the cell voltage bounces back higher when discharge is stopped. This corresponds to a discharge amount of less energy, and does mean that there’s energy left in the cell. So if I selected the cell with the highest bounce back voltage (ie the cell that was discharged at the highest current), then discharged it to 2.8V at 0.2A, I’d still find that there was a lot of energy still in the cell.

These cells bounce back to 1.5V immediately, in almost every case. That’s good and bad…. checking these cells on a multimeter might give the impression that they’re full or at least not empty. So this could be a frustrating aspect to these cells.

Charge Test

I couldn’t test these cells on my cell tester, so I tested charging on the Nanfu charger in all the ways I normally test a charger.

Charging is… interesting. It seems like the charger puts ~5V across the cell. I have no idea why that is or how exactly it works. But that certainly has a lot to do with why to not charge these cells in a li-ion charger. To wit- it shouldn’t hurt the cells (possibly but I don’t recommend trying), but it just won’t charge them because it’s not hitting the voltage they need. The current looks very normal though, at 0.5A for the CC phase.

Just for giggles I also logged the power going into the charger across the USB to micro-USB cable. This is for just a single cell in the charger.

Conclusion

Hmmm conclusion…. Well these cells do absolutely do what they claim. I think that’s good and cool. It’s cool that these exist. But as for use, I don’t know what application I will use these in. I certainly don’t want to use them in devices that have their own built-in charging (XBOX controller for example). Also the voltage supply and cutoff being so sharp could be nice for unregulated flashlights. The cell would act as a bit of regulation.

Also the price…. I can buy a pack of 4 NiMH from Ikea for $7, and they don’t require any special charger. So at $35, they’re decidedly expensive.

But if you know a use, and have a good use, then these are great cells!

Notes

These cells were provided by Nanfu for review. I was not paid to write this review.

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