With 6000 similar ELT units in service it would be hard to believe that this was the first one to sufffer a battery problem.
It would be interesting to know how many batteries have been replaced, per qouted 10 year life any replacement would be a failure not end of life.
The really ineresting question would be the condition of the replaced cells,
what if failure is "rare but happens" but on metal aircraft "thermal event" energy is insufficient due to heat sinking etc to light a fire or even be noticed?