backup battery model

[epsilon]

Hello,
I have Qtek 2020 w/o a backup battery, so i need one.

Can anyone tell me what bettery do i need?
What is the backup battery model in HTC Himalaya?

And maybe someone know where can i buy it in europe?

[epsilon]

Maxell MLxxxx (seems to be 2016) 3V.
where can i get it?