21 pieces, wow your house must be huge…
Thought I’d share my little setup with some Teclast P80h tablets here. They’re extremely cheap (cost me 36€ with local 2 day shipping off ebay), have decent bezels and quality and a neutral-looking flat-backed case.
Since I didn’t want to have an assortment of always-connected chinese LiIon batteries around the house, I run them straight off power, with wiring and attachment hidden out of sight.
I place them on regular wall cans - in there goes a small USB charger (1A does the trick, old iPhone chargers are ideal because they’re small, safe and provide good power quality)
Next I pop the back off the tablet, running a fingernail around the edges to pop out the attachment clips is enough. On that goes a hole for the power cable, and two screw holes lined up with the holes of the wall can. Two screws (make sure their heads aren’t too bulky!) attach it all.
Next i remove the battery - the glue strips have pull tags to remove them from under the side of the battery, then unsolder the 3 cables, careful to not short them!
On the B+ and B- pins goes my power cable - these tablets don’t mind running directly on 5V instead of their battery, and will just indicate a 100% full battery.
The newer Android 7 versions from Teclast can be configured in settings to never go to sleep, nice. However after removing the battery they’d complain the battery is too cold, because of the missing sensor. Solder a 10kOhm resistor between B- and the NTC pin to make it happy again.
The older Android 5 versions don’t have the option to never sleep, BUT there’s the System developer option to not sleep while connected to power. To make it think it’s plugged into USB, we need to connect the USB 5V pin to our power supply as well. There’s a convenient soldering pad marked VBUS right behind the USB plug - connect it to B+ with the thinnest wire you can find to not put any stress on the tiny solder pad.
If you’re worried about privacy and don’t need the cameras and microphones of the tablet anyway, you can disconnect their cables easily, everything will work just fine without them.
Now let’s put it on the wall and snap the case back together, ready for HABpanel!
Power consumption when the tablet is idle showing the UI at low brightness runs around 1,5W
bricked my p80h today, what a waste of time 
Ha, what happened?
followed this tutorial and after flashing twrp i couldn’t boot into recovery mode but could watch the tablet reboot endless times while telling me
Orange State
Your devices has been unlocked and can't be trusted
Your devices will boot in 5 seconds
apparentely there’s no solution to this 
My first tablet was P80. It lays open on my desk as it refuses to charge. This problem existed from the very beginning if I let it eat all the battery and power off. I will try to solder power directly instead of battery, would be great if it works.
My second tablet is this one.
Decent, but HabPanel with Grafana webviews does not work that fast as expected under Fully Browser. I see that RAM and CPU is not fully utilized.
Mounting was done the way Artyom_Syomushkin did it.
My P80 (without H) is dead
I tried booting it with voltage regulator and using 3.7 then up to 4.8V. There is a small voltage drop when pressing the power button but nothing else. Any tips? (bit off topic)
I also have a Teclast Tablet which I used for a while as Habpanel.
The drawback of these devices is the display, which has a plastic surface and gets easily scratches. But ok, for this price 
The other thing is, that mine started to have graphics problems after running always on for months. I seems to be a hardware problem in the LCD driver, display then is unreadable.
So I replaced it with an ACER tablet which now runs fine. The Teclast still works as a normal tablet, but it seems not to survive the always-on mode.
would you tell us which one?
Acer Iconia One 10 B3-A40 Tablet, 10,1" for 129€
I’ve had one of those running as an “always-on” wall-mounted tablet for two years. In two years, I only needed to reboot it once.
I too have several tablets used for paperweight and I would like to use them as always on display. However all of their batteries are expanded from it’s original size because of aging or overcharging. How can I use them without battery?
EDIT:
my devices are:
asus padfone S
samsung galaxy tab 7.7
samsung galaxy tab 10" (forget the model)
iphone 3gs
iphone 4s
You could potentially remove the batteries and connect power adapters directly to the circuit boards, but if you don’t have experience working with electronics then I don’t recommend it. Shorting out power wires is an easy way to cause a fire. Alternatively, you can possibly still get replacement batteries for some of those devices, in which case you’re not messing around with direct power.
Whatever you do, don’t plug in any devices with bloated batteries. I think you already know this, but I’m saying it anyway as many people don’t realize how dangerous it is to charge a battery that’s losing its integrity.
Having old tech laying around annoys me as well, but you might be better off finding an e-recycling program and just picking up an Amazon Fire tablet.