Well, yesterday’s capacity remained a little unknown, but the tablet was still on at night. Today after factory restart, the capacity was 23%. I only charged it for one hour before trying. So, maybe the guess is right, but also maybe not.
Most tablets are like any other Android mobile device you put them in recovery mode and reset them using the existing factory firmware. You only plug them in to make sure they are in power mode and not on battery. I’m not sure where the Telnet stuff is coming from? 
True. But as you can see in Jolla instruction, this is how it is supposed to work. Luckily it worked at last, even without any changes in EOS setup. Executing factory reset reverted back to very early version. Then I needed to upgrade half a dozen times to reach the latest version. I only lost some “hard to get” apps, but hopefully I can still find them somewhere.
Yes, i do see this and now it makes sense. What you originally asked didn’t at least to me… This is standard recovery setup built into it. It’s just connecting to an IP address using telnet and recovering from there using the computers connection in a recovery mode.
2 Setting up Recover Mode for the first time
These instructions are for setting your Windows-, Mac- or Linux PC up to be able to use Recovery Mode, and to teach you how to put your Jolla Tablet into a suitable mode for Recovery Mode.
2.1 Preparing your Jolla Tablet for Recovery Mode
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Switch off your Jolla Tablet
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Press and hold the Volume Down & Power buttons. Keep them held down until you see a Jolla logo on the display of your device.
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In a moment you will see a view that reads “Droidboot”, and a menu with the selection “Recovery”. Move the selector to “Recovery” by using the volume keys. Confirm your selection by pressing the Power key.
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Soon the text “RECOVERY: Connect USB cable and open telnet connection to address 10.42.66.66” will appear on your Tablet’s screen.
Your Tablet is now ready for Recovery Mode.