A pair of UltraFire TR17670 1800mAh 3.7V batteries and a little DIY.

I have an ESR meter built from a circuit designed by GO, a fellow member of the pro-radio forum. I’m sure some of you use this meter too. I use it all the time, but when it’s powered by a 9V battery with the display backlight on, it drains batteries pretty quickly, so I decided to order a couple of rechargeable batteries for it. Details below the fold.

While browsing the ChinaBay site, I naturally looked at batteries too. I find the subject very interesting, and there are plenty of battery reviews and tests here as well. But the 17670-size batteries caught my eye: they’re only a millimeter different, but two of them add up to 2 mm, and when I measured the case I planned to put them in, 18 mm just wouldn’t fit.
At first I thought it was a typo and they were actually 18 mm, but let’s take things in order.

I’d read that lithium batteries can have delivery problems, so I was worried, but there was no need: everything arrived without a hitch.
The batteries came in a regular yellow envelope, wrapped in bubble wrap.


They were inside another little bag, so the packaging was neat enough. No complaints.


As mentioned above, these are 17670-size batteries. The labels also say they have over-discharge and overcharge protection, thanks to a protection circuit built into each one.
We’ll test that later.


The battery dimensions are a little off. According to the markings, they should be 17 mm in diameter and 67 mm long. In reality, the diameter is as specified (that was the important part for me), but they’re only 65 mm long.




Each battery weighs 36 grams.


Naturally, the next thing I wanted to do was test what I’d received. I don’t have a dedicated tester at home, and I didn’t feel like bothering a friend who does this professionally, so I decided to check the capacity using the lab power supply I’d recently built, since it can measure the capacity delivered to a load.
It can’t discharge batteries, so I first discharged them manually. By the way, they arrived almost fully charged: under a 1.8 A load, the voltage was about 3.42 V.

And this is where I ran into a problem. As I mentioned above, the batteries were advertised as having protection circuits, but in fact they didn’t. I was able to discharge the first battery down to 2 V without anything cutting out, and didn’t discharge it any further. I only discharged the second one to 2.6 V. For obvious reasons, I didn’t test the overvoltage or short-circuit protection either; it was already clear there was no protection at all.

There are lots of photos, so I’ve tucked them under a spoiler.

So, in reality, we have batteries with a capacity of about 1.32 Ah (at least they have the same capacity; it would be worse if they were different), despite being rated at 1.8 Ah. And that's without accounting for the battery's efficiency. Lithium batteries are of course much better in this respect than nickel-cadmium and nickel-metal hydride batteries, which need to be charged with 1.5 times their capacity, but lithium still isn't 100% efficient.
So I'd say the actual capacity of these batteries is closer to 1.2 Ah, i.e. just 2/3 of the claimed capacity.

But I got curious: maybe there really was a protection board and I just hadn't understood something. A small cut with a utility knife showed that there definitely wasn't a board. All that cutting for nothing.


So, that's a bit of a disappointment. At the advertised price of $9 for the pair, I expected better.
People often write here that stores send one product for review and sell a different, inferior one.
The Xiaomi power bank is a case in point; this has come up more than once. In my experience, it's almost the other way around. In my USB thermometer review, the one they sent me was worse than the one I bought (as people pointed out in the comments). Here's another example: batteries with less capacity than advertised and no protection board.

I planned to use them in a homemade C-ESR meter, which I use quite often. Since I fitted it with green glass (there wasn't any clear glass, and I didn't want to leave it without glass altogether), you can't see anything without the backlight. In short, it eats 9 V batteries like crazy.
Yes, it's time to buy something more substantial, like an E7-22, but when I look at the price tag, my inner cheapskate lets out a plaintive squeak and won't let me buy it.

For enthusiasts and soldering fans, the rest is under the spoiler.

Then it was the usual routine: I selected the components, routed a small PCB, and etched it.


I selected the parts to match the planned circuit; I bought some and used others from my stock.
Most of it came straight from the IC datasheets.


The result is this rather nice little board.


It's also quite compact.


I got everything ready for the conversion.


This is what the device looked like before the conversion. It drains 9 V batteries at an impressive rate.


I cut a small hole in the side of the case for the connector and attached the board with double-sided tape. The batteries fit perfectly and are held in place by the case, so everything worked out great.


I tested it and put everything back together. A LED next to the connector indicates that the device is charging. Another LED on top of the case indicates that the battery is discharged. Everything works great.



So, here's my take.
Pros.
Honestly, I don't even know what to put here. I did find a use for them, so they may well have a place after all.

Cons
Capacity is lower than advertised
A protection circuit is listed, but it's actually missing.
The price could be lower. I think it's way too high, especially considering the previous two points.

I probably wouldn't buy batteries like these, unless I really needed the 17650 size. The store chinabuye provided these batteries to me free of charge for testing and review.

I hope you found my review useful. If you have any questions or suggestions, I'll be happy to answer.