[Teclast X98 Air 3G] motoi_bogdan:
here are some photos with the guts of this tablet

As you can see, the C9J8 at least has some metal shield above the cpu area and some crappy thermal compound over it. Some older models lacked the metal shield.

Next we have the battery wires and their link to the motherboard. As you can see, left to the 3 wires there are 4 brown devices, mounted in parallel. Those are capacitors. Like i've said above I'm thinking of adding some aditional capacitance to further help the motherboard compensate for the voltage drops registered on high load scenarios. The chinese guys thought of that, added the 4 caps but deemed them enough. Noup, that's just barely doing it. In fact the whole design is made to a price point, that's to be expected.

For easier probing, I've disconnected the red positive wire, and added a piece of wire of my own, one end to the battery red wire the other to it's coresponding pad on the motherboard. At the end of my wire, i'm probing in series with an ampere meter.

And for the sake of it, here's a photo with the registered power consumption with the tablet on. 1.11 amps x 3.8 volts = 4.21W total power being drawn. Actually that's pretty good. I remember the days i was probing a htc hd2 for some cpu related problems. While doing a benchmark at full brightness that device draw a maximum of 5.5 W. Due to the recent advancements, now we see a tablet drawing only 4.2W (admited, it's not on full load, but the screen is also much larger).

Anyway let's get back to our problems.

1. The high power drain when the tablet was off can be solved in the same way as fixing the reported battery capacity. Like previous guides made, you need to fully discharge the battery and then charge for 8 hours with the tablet OFF (don't turn it on). I had to do this 2 times to get the thing to work.

2. 7% battery and 1 cell reported. Like i've said in my first post, i've tried to let the battery discharge and then recharge while turned off. It never work. However, after desoldering the battery wires from the motherboard and then soldering them back (power was cut off from the motherboard during that time) now after my first attempt to discharge/recharge the battery, the capacity and number of cells are reported correctly for the first time since i've had this tablet. I now have to discharge the tablet again to see if it will get stuck at 7% again but at least i get the capacity reported like it should.

2. The shutdown/freeze under load. This thing ocured to me several times in the past but for whatever reason the tablet doesn't do that anymore. Arghhh.... Anyway, if anyone has this problem and knows how to reproduce it in windows (i'm only running windows now) please do tell me in order to test some solutions to it. My first try is to add some capacitors over the main power rail. If this will work, i'll then design a capacitance multiplier circuit using some transistors since there is not enough space in the tablet to simply add capacitors.

3. High standby drain. In my best scenario, the tablet draws 0.3 to 0.5 amps in standby and that's huge. I've tried disconnecting various devices on the motherboard but all that power goes into the cpu area. It has to do with the cpu core voltage and stand by states. The cpu is simply not sleeping deep enough. However that should be fixable with a bios update if teclast should decide to bother with that. One problem though, it seems not all tablets have this problem. But since it's located in the cpu area, if it should be a hardware fault there is no practical diy fix for that.