Battery holder footprint

[SolarSunrise]

Hello again. I am currently designing a device that is powered from two LR44 coin cell batteries. The data sheet from the battery holder manufacturer says I need minimum 4mm by 4mm copper pad for the negative contact (check image below).

But won't this create an unstable connection? The diameter of a standard LR44 is about 11mm. The height of the plated copper would be lower than the surrounding solder mask(or is it?), thus the bottom of the coin cell won't contact the pad. Unfortunately the data sheet has absolutely nothing related to solder mask expansion and all the important bits. Do I have to make a HUGE solder expansion to keep the solder mask out?

The reason I'm really picky here is because as always, there's nothing more excruciating than having a production run of 1000 faulty boards... And this is my first design that had coin cells (never had to use one of these boys before). Just trying to avoid Murphy.

Thanks a lot guys!

[free_electron]

Open solder mask for the entire size of the battery.

[SolarSunrise]

Can a moderator remove this thread? I made a new thread in the general pcb design genre when I realized this thread was in Altium Designer section.