I’ve had an unusual number of leaked batteries in the past year. Before, it had been at least a decade since any leaked. There have been at least four, two of which were Duracell; the others Eveready. Eihter AA or AAA. In all cases it was in gear that was turned off (physical switch) and sitting unused in a drawer or on a shelf, inside the house. No temperature issues. I went to use them, found them dead and noted a lot of leaking once I opened them to change the batteries. All of which used at least 3 cells in series. That is, they were in battery trays that wire them all together (but the devices had hard power-off switches).
Can’t pin down the purchasing source but it’d have been either a local Home Depot, CVS or Costco.