Sorted. Duracell manager is sending a prepaid UPS container (and Duracell vouchers, just in case I wanted to risk another episode... hehe) and is issuing ample compensation upon receipt.
All this advice about checking batteries periodically is correct, yes, but unless one has OCD, come on - who actually has "must check torch batteries this month" in their calendar? I have a life, and expect all their "research" to have amounted to a product able to contain itself upon failure, after all these years on sale.
The horse has bolted; thankfully the cowboys are about to round it back up