1.5V Rechargeable AAs and a Kevo lock

Until very recently, if you wanted rechargeable AAs you were stuck with NiMH batteries, which topped out at around 1.2V (Rechargeable Batteries — compared and explained in detail). Off the shelf alkaline AAs, though, at least started life as (at least) 1.5V cells:

New Energizer alkaline AA battery, 1.5V

As the battery was used, the voltage decreases over time.

In 2014 I installed the first generation Kēvo smart deadbolt, and loved it. I got a set of rechargeable AAs and recharged them every few months or so and life was good. Until life happened and in 2019 I had to replace that lock; the only one available was the Kwikset Kēvo 2nd Gen.

That lock is much more finicky. It would work on NiMH rechargeable AAs, but only for a short time (a matter of days), and immediately started complaining the batteries were low.

Meanwhile, e.g., a set of (4) Energizer MAX batteries, packaged in November 2021 and bought and installed in mid-December 2021, lasted about 2 months. When I tested them with my ultra high end digital multimeter, the “dead” batteries measured 1.48V. The brand new batteries registered 1.62V, a drop-off of about 0.14V (~9%).

The lock really wanted a full 6V. (And yeah, I checked all the cables, and the bolt isn’t binding on anything and moves smoothly and easily, and I’ve reset the lock, and ...)

Recently, 1.5V rechargeable AAs have emerged. The first I’m aware of are the Tenavolts ($35 for a 4-pack, with a charger), which launched via Indiegogo and started shipping in early 2019. Sure enough, these read just over 1.5V:

Brand new freshly charged Tenavolts AA, 1.53V

I installed the Tenavolts in late May of 2022 and the lock took them happily. Tested them after a few months and they were still showing > 1.5V. They lasted about 7 months with no indication of low battery life until, one morning, the lock sort of went haywire (showed an LED light sequence I’d never seen before) and tehn was completely dead.

I pulled the batteries out to test and, sure  enough, they read 0V. That’s exactly what I expected based on the manufacturer’s claims (“ Tenavolts outputs 1.5 voltage from 100% to 0% electric capacity”), and this in depth analysis.

 

I pulled them out of the lock and tossed them into their charger for a few hours and now they’re good as new again:

 

Tenavolts recharged, showing 1.52V again

 

(Running them empty can’t be good for them, so maybe I’ll set up a 6 month repeating reminder to charge them proactively.)

 

I’m quite happy with the Tenavolts, but since then there has been a flood of 1.5V rechargeable AAs hitting the market. I picked up these EBL AA Battery 1.5V AA Lithium ion Batteries 3300mWh batteries (4 for $24) which have built in microUSB ports for recharging (there’s no need for a separate charger). I use these in my Logitech Bluetooth mice (M535, M557, M350 Pebble).

 

Now I’m wondering if these new 1.5V AAs will work well with the Bose A20 headset...

Edit: A few cycles in and things are still pretty okay with the Tenavolts. I’m seeing 6.14V with (4) freshly charged Tenavolt AAs in series, vs. 6.48V with (4) brand new Energizers:

Energizer alkaline AAs x4: 6.46V

Tenavolt 1.5V LiIon rechargeable AAs x4: 6.14V