Yesterday I noticed that my Pi-Top wasn't running from the integrated battery anymore. Only if I plug in the AC adaptor the Pi-Top's hub will provide power to the Raspberry Pi. This is a huge problem for a computer that is meant to be used as a mobile computer.
Instead of sending it back I decided to open the Pi-Top's battery case and try to find the error myself. As the title suggested, I found it: One tiny screw. But first let me tell you how to open the battery case.
When you have disassembled the Pi-Top you will see a metal plate in the bottom case. Below that metal plate is the so called "smart battery". The red stripe is a piece of isolating tape I added to avoid my Raspberry Pi having a short circuit on that metal plate. I'm running the Pi-Top with a Raspberry Pi Model B that doesn't have the holes to tighten it with screws on the "rail" in the bottom case of the Pi-Top so it's more or less held in position by the USB and HDMI cable.
The screws for the battery case cannot be opened with the tools provided with the Pi-Top. However, an alligator wrench will do the job if you press it gently onto a screw and then turn it counter-clockwise for one turn. After that you can use your fingers to get the screws out.
The screw on the battery connector is a bit special: You don't want to put too much pressure on the alligator wrench since you want that screw to mount the Pi-Top's hub onto it after you have put the metal plate back in place.
Now use a flat screw driver to lift the metal plate. Start from the battery connector and move to the right, gently lifting the metal plate. Be extremely carefule since there are lithium polymer cells below the metal plate!
The battery management system is tightened to the bottom case by three tiny philips screws.
You see that there is one screw missing. The hole has become wider than the screw so that the screw originally in that hole became loose and started to move freely inside the battery case. While lifting the metal plate with the Pi-Top's bottom case held upside down it fell out. It may have created a short circuit or caused a fuse to break a circuit inside the battery management system or it could have made some other sort of bad connection that caused a part in the battery management system's circuitry to fail.
The only imaginable reason why the hole of the screw has widened was mechanic pressure that caused the screw to become loose. Mechanic pressure that may be applied to the Pi-Top when it is carried in a rucksack with other stuff that weights a few kilograms (which happened several times in the last weeks). But if a portable computer would be that sensitive, my Laptop would have been broken a long time ago. Well, it is ten years old and still working (more or less, but that's another story which is not related to carrying it in heavy rucksacks).
Hopefully the "smart battery" in the Pi-Top is smart enough to recover from a short circuit or other problems caused by one tiny screw. If that's not the case I think I will have to replace the bottom case of the Pi-Top since the batteries are integrated into the bottom and they're soldered directly with the battery management system so that I can't just connect a replacement battery management system.
While writing this I'm charging the Pi-Top's battery. For now there is no energy coming out of the Pi-Top's battery since the power button LED goes off almost immediately when I unplug the power cable. So this is a bad sign. If normal charging doesn't work I have to measure the cell voltage of each Li-Po cell of the Pi-Top's battery and charge them manually (via a charging station) if at least one cell has undervoltage. If the battery management system itself is broken I have a bigger problem: Four unusable fully-working Li-PO cells and no mobile computer.
If I have to replace the bottom case of the Pi-Top I'm already thinking about printing my own bottom case and integrating other batteries. For that I have to find out on what voltage range the Pi-Top's hub operates. Then I can choose what kind of batteries I'm placing inside the self-made bottom: Either Ni-MH (because they're robust) or LiFePO (because they're robust and have a high capacity). Of course, the new bottom case would be higher than the old one so that the Pi-Top as a whole woud become more thick. But this gives me the opportunity to place standard size batteries inside the Pi-Top. Maybe some Mignon-sized (AA sized) Ni-MH cells will keep the Pi-Top running a few hours, too :)
I would also need to know the pinout of the battery connector and find/build a compatible battery management system etc. A lot of work which would solve this problem but which is hard to archieve if you're doing it alone... maybe some other Pi-Top user has the same problem and is willing to help?
Appendix: Putting the battery case together again
While putting the battery case together again make sure the little rubber "plates" on the metal case stay in place!