Would the furnace be able to contain it just fine, or would it explode, or would the flaming battery juice melt through the hull of the container, or what?
You don’t burn the coffin during cremation
As a result, you’d end up with a bemused mortician the next time they used the coffin, and that’s about it.
You don’t even get in a coffin these days. You get taken straight from the place you died into the oven.
? Usually they are intended as part of the fuel needed to burn the body, at least here in DE.
There actually exists a study done in Japan, combining both a survey of crematoriums and experimental tests using a crematory retort and sample medical device batteries.
The results found that the device explosions were audible, but did not damage the experimental crematorium. In the survey, however, 92% (in 2012) and 51% (in 2013) of questioned crematoriums reported “damage” from medical device batteries. The cause for this discrepancy is unclear; it’s possible those answering the questionnaire considered scorching, scratches, or metal residue to be “damage”, while the test only looked for “structural damage”.
30 phone batteries is a lot more than 8 medical batteries, but it’s still not a whole lot. Compared to, say, powerbank or scooter batteries, which can go up rather more spectacularly, the effects are more limited.
tl;dr - it’d probably be noisy and some refractory bricks might need replacing, but it probably wouldn’t blow up the retort.
