Battery for the Teclast Tbook 10S tablet

Three and a half years ago, I reviewed the Teclast Tbook 10S tablet. I really liked it at the time, and it saw fairly heavy use for almost the entire period after I wrote the review. But after about two and a half years, its battery started to give out, and by the three-year mark it was basically running only on mains power, so I decided to replace it with a new one.


It’s worth mentioning that the tablet ran on mains power most of the time, but occasionally I needed to take it somewhere. The battery had enough capacity that its gradual decline went unnoticed, but after about three years the drop became critical, and after three and a half it would literally run for only a few minutes. In short, it was in really bad shape.
At first I wanted to order a battery, or at least find one locally, even if it had a lower capacity. The main thing was that it could run for a while. But I immediately ran into two problems:
1. The battery voltage isn’t the usual 3.6–3.7 V, but 3.8 V, meaning the charge termination voltage is 4.35 V.
2. Judging by the markings, it’s 2.6 mm thick.

Taking both of those things into account, I realized that finding this kind of battery locally was close to impossible, so I started digging around on AliExpress. In the end, I found two sellers offering batteries that not only matched the specs, but were specifically listed for the tablet model mentioned above.
I didn’t like one seller—or rather, I didn’t like the reviews for their products. The other seller had noticeably better reviews, so I decided to order from them. It came to $19.50 including shipping. Exactly two weeks passed between placing the order and receiving it, and the courier eventually brought me a fairly large box.

No complaints about the packaging at all: the battery was wrapped in a generous amount of bubble wrap.


The package included a set of various opening tools, a couple of screwdrivers, a keychain, and two thin plastic strips. To my embarrassment, I have no idea what those are for.


The battery looks like the one installed in the tablet, though I’m going by the photos from my review here, since I didn’t want to open it up again unnecessarily.


The original cells were marked 2663135: 26 is the thickness, 2.6 mm; 63 is the width, 63 mm; and 135 is the length, 135 mm. Since the battery consists of two cells, its overall dimensions are 126 × 135 mm.
The length and width are spot on, but the new battery is slightly thicker: 2.7 mm versus 2.6 mm for the old one. On top of that, it’s even thicker where the protection board is located.


Each cell has markings, though they’re a little odd and partly crossed out for some reason. Interestingly, the cells also have something like a matrix code, and each one is different. Could it actually be something branded, even if not original?


The protection board is wrapped in tape, and the wires look thin, although the original ones were about the same.


The battery impedance, including the protection board, is 37 mΩ. I measured it using a four-wire connection; fortunately, the battery itself has two wires for each terminal.


Before installing it, I decided to measure its capacity after all, using an EBC-A10H battery tester.


But first, here’s how the battery behaves while charging. There’s a small mistake here, which you can see in the graph title. Looking at the original 6000 mAh battery, I somehow assumed the new one had the same capacity and ran the tests on the basis that 1C = 6 Ah.
Charging from fully discharged to 4.35 V, with a 0.17 A cutoff current, took almost 4 hours.


In case you’re wondering where the 0.17 A cutoff current came from, here’s the explanation. When I did the initial charge, I didn’t expect it to take so long, so I eventually had to stop it manually at 0.17 A. I used that value for all the tests afterward.


Capacity at currents of 0.2, 0.5, and 0.75C, or 1.2, 3, and 4.5 A.
I was genuinely surprised when the battery exceeded even its rated 7000 mAh, delivering 7124 mAh, or 26.85 Wh. By the way, regarding the latter figure, the cells are marked with a capacity in Wh: 13.3 Wh, or 26.6 Wh for the whole battery. I measured 26.85 Wh, even with the protection board included.


I didn’t run a load test on the protection board, but it shut off fairly quickly at 6 A.


What concerns me most for now is whether the battery really is rated for 4.35 V, rather than being a relabeled 4.2 V battery—especially since the CV phase during charging took a very long time. As an additional test, I tried charging it to 4.2 V, and it turned out there was hardly any difference. With a cutoff current of 0.2 A (I got tired of waiting), charging took 3.5 hours.


And then it was the usual routine: after briefly remembering the tablet designers with a few choice words, I took it apart. The original battery is attached with double-sided tape, plus fabric tape around almost the entire perimeter.


The new and old batteries side by side. To me, the old one looks neater. One cell has already started to swell; the other is still holding up, but I don't think it'll last much longer. The old battery weighs 95 g, compared with 110 g for the new one.


The connectors are identical, but the wires on the new battery are a little longer. Just to be safe, before installing it I peeled off the tape and routed the wires underneath more neatly to reduce the thickness in that spot.


I partially removed the old double-sided tape, applied new tape, installed the battery, and secured fabric tape around the perimeter.
In fact, all I needed for the repair was what the seller included in the kit, though I had to sharpen one of the “opening tools” with a needle file.


I put it back together, plugged it in to charge, and checked that it worked. In the comments on another seller's listing, I saw a review saying that after the battery replacement, it wouldn't charge to 100%. That's one indirect sign that the person installed a 3.7 V battery instead of a 3.8 V one. I didn't have that problem: after charging for a while, it displayed 100% without any issues.


Well, what can I say? So far, I have no complaints. The packaging was good, the battery matches the specifications, and the tablet really does last about as long as it did when new, maybe even a little longer.
The only thing I didn't like was the messy wire routing near the protection board. It probably would have fit as is, but my inner perfectionist wouldn't allow it. The battery itself is 0.1 mm thicker than the original, but that made no difference at all; there's a little extra room inside.

In short, I can definitely recommend the seller, but of course, read the reviews first, if there are any. By the way, when ordering, I recommend checking the seller's reviews for other products too; they may contain useful information about quality and customer service.

That's all from me. I hope this was useful.