Key Fobs

[Judders]

I've bought a 1991 300TE. Two alarm fobs were given to me and I was told the batteries were dead. The LEDs light but there is not enough power to set the alarm (seemingly).

I have tried to open them up to look at the battery but it doesn't seem to want to open. Should I force it or is there another way?

Is it a Merc specific battery?

All help gratefully recieved.