My Nexus 7 (2012) is online again (with lineageos and external battery)

In 2014 i did the last update for my Nexus 7 (s. here).
It was the last update which was provided by Google for this device:

• Android Update 5.0 (11.2014)
• Android Update 4.4.3 (6.2014)
• Android Update 4.4.2 (12.2013)
• Android Update 4.4 (11.2013)
• Android Update 4.3 (8.2013)
• Android Update 4.2.2 (2.2013)
• Android Update 4.2.1 (12.2012)
• Android Update 4.2 (11.2012)
• Android Update 4.1.2 (10.2012)

I bought the Nexus 7 seven and a half year ago and on the weekend i found the tablet in the back of the cupboard. It did not work, because the battery was completely discharged and the device refused to charge it.
Without a battery it is not possible to startup the device - only power over USB is not enough.

So i disassembled it like described here and added some cables to connect a battery from outside:

And with that modification i was able to start it  - but running Android 5 with 8GB disk space is no fun.
So i booted TWRP onto this device:

root@zerberus:~/bin# fastboot oem unlock
                                                   (bootloader) erasing userdata...
(bootloader) erasing userdata done
(bootloader) erasing cache...
(bootloader) erasing cache done
(bootloader) unlocking...
(bootloader) Bootloader is unlocked now.
OKAY [193.432s]
Finished. Total time: 193.433s

root@zerberus:~/bin#fastboot boot  ~/Downloads/twrp-3.0.2-0-grouper.img

After that i was able to install lineageOS via adb sideload.

 adb sideload  ~/Downloads/lineage-14.1-20171122_224807-UNOFFICIAL-aaopt-grouper.zip 
 adb sideload  ~/Downloads/open_gapps-arm-7.1-pico-20200415.zip 

Now the device has nearly 6GB space left:

 

 I can use the play store and the device runs on Android version 7 - and it runs youtube movies without any interruptions...