Coin Battery for RTC within ATEX Zone 2 or Class 2 Div 2

[riscy]

Is there a guideline about lithium coin battery for real-time clock mounted on the board within a diecast IP65 sealed box (about 150x150x150mm) within Class 2 Div 2 or ATEX Zone 2 (ie dog-house). Does it require further mitigation measures (ie pressure vents)? I have put a small fuse on the PCB in series with the battery.

 

[3DDave]

My experience is that the main thing that is required is to prevent, in the use of lithium PRIMARY cells, that they never get exposed to an external voltage that could drive current backwards. In general the surface area to volume is such that a short circuit will exhaust the chemistry inside them faster than the heat can build up to cause rupture.