Sending Gameboy and Gameboy advance cartridges through royal mail?

At the current moment on ebay I am selling some old games I have knocking around (9 gameboy advance and 4 gameboy games) and I did a little research on royal mail's website and it seems they have certain restrictions on batteries in electronic devices. According to them "Each package must contain no more than four cells or two batteries installed in equipment." Assuming each game cartridge contains one single button cell that would limit me to packaging 4 games in any given parcel right? (If this is true I'm going to be quite upset at having to send one parcel with only 1 game inside since I'm selling 13 total).

Now I'm unsure of what they think qualifies as "electronic items" so I'm uncertain of whether it would be ok shoving all 13 of the games I'm selling into bubble wrap and into a parcel bag. Would this actually be acceptable assuming everything is packaged alright?