787 fire investigation looks at pinched battery wiring | Business & Technology | The Seattle Times
"The two sources suggested that Honeywell might have replaced the batteries at some stage before delivery of the jet because the devices sat on the shelf during the years-long 787 program delays."
Sat on whose shelf? Are these ELTs 787 specific parts? Or are they used across various models? If its the latter, then I'd expect Honeywell to pull stock and ship it as various orders came in. If the 787 program was a couple of years late, they'd ship units built later on.
If it was Boeing's shelf, then who replaced the batteries? If Boeing took possession of the units and shelved them, then they'd be responsible for maintenance. Seeing how this was not standard in-service fleet maintenance, who did they send into the warehouse, screwdriver in hand, to swap the batteries?
Given several possible scenarios, this looks like it could be a maintenance procedure problem. Airlines take steps to make sure that work is performed by qualified personnel. because this is a part of their normal business function. But out of sequence manufacturing or maintenance can be a planning headache.