Frequent Traveller,
I can't see how the Stainless Steel casing has in any significant way changed the occurrence probability of 'Battery Unserviceable' as an EVENT
You are right, the box makes no differnce to the probability of a battery failure. The issue is the batteries will fail at some point. They are not 100% reliable, nothing is. The Li batteries have a high energy density so when whey do fail the fire etc must be contained.
statistics show some 130 such events in 50,000 flight hours
Apparently most of these events were due to excessive discharge while on a ground. When an LI battery is discharged below its minimum level it should not be recharged up to normal levels again so it is replaced. I am not an expert on this but some smart people earlier in this thread explained this. This is not a safty issue.
what is the duration of 'change battery' as a line maintenance task ?
I have no idea. I am sure it will be complete pain in the ar_e to service but this is not a safety issue.
does this imply an aircraft change ? ... whence the possible concern of Underwriters ?
I have no idea.