Featured No boat for you

A charging and discharging lead acid battery is both an electrolyser and a chemical conversion device changing the ratio of sulphur in the electrolyte, transferring it in or out of the lead plate.

I suggest you actually take the cap off a flooded cell lead acid battery and watch the bubbles produced during discharging as well as charging. Having worked with the things for 40 yr in the trade, I've seen enough explode during engine cranking.
There was a spate of "car bombs" that blew front mudguards and bonnets off car when first cranked over on a winters morning in Australia. The cause was finally narrowed down to a new battery developed by Dunlop I believe. It was called a Pulsar battery and made in vertical layers, much like the new blade batteries, but lead acid. The problem was narrowed down to poor resistance welds between the plates, creating heat and finally a spark that ignited the perfect mix of hydrogen and oxygen.
If you doubt just how much explosive power is in this mix, consider that an internal combustion engine will run on it if you can produce enough.

Referring to the graph on page 11 comparing the percentages of each gas, then the percentage of that gas compared to the total vapour ejected from the cell vent ..... how can you consider that represents 50% of what is ejected, even if you want to narrow it down to gases, ethene is more than double all the other gasses they actually measured. There is no mention of whether there were any other gases involved in the huge amount of "other" that makes up the total ejected from the cell during venting.
It might be interesting for you to read how the test was conducted and temperature involved in the test .... do you really believe the LFP cells experienced over 230*C while charging, check fig 4 and 5 page 7 and 8 .....

You could be right about the PEBCAK ...... but maybe not this end ......

T1 Terry