SW6 microswitch is used to set the language version – please see page 29 of the user manual (document available in the documents section above). DIP switch 4 of that switch must be set to OFF or it will be impossible to enter BASIC.
The original battery seems to be NiCd 4×1.2V 480mAh. Please see the Tips and Tricks document on the battery replacement recommendation. It is possible to run the machine without any battery, but not with the original power supply, which would provide to high voltage. A regulated external power supply worked well and the voltage range of 5-7V was right to power the computer, however with lower voltage levels it will have troubles operating the printer and tape recorder.
The LCD display module of Epson HX-20 is right above the battery compartment and leaking battery damaged the traces on the board and the connecting tape. There was enough length of the tape to solder the wires to the board – these wires come from an IDE HDD tape. It is possible to solder the wires directly to the tape – the tape will not melt with soldering temperatures up to 350 centigrades.
The non-thermal printing paper ribbons are broadly available today. The ink cartridge is still manufactured by Epson, its symbol is ERC-09.