Duracell Plus 9V (4-pack): 6LR61 alkaline block batteries for smoke alarms and more

The pack contains four 9-volt block batteries, known as PP3 or 6LR61 under the IEC standard (Duracell code MN1604). They are alkaline cells from the Plus range with the usual snap terminals on top, so they fit any 9V compartment.

Duracell describes the Plus 9V as an everyday all-rounder, for example for smoke alarms and remote controls. According to the manufacturer it has a long shelf life and performs reliably at low temperatures. Besides smoke alarms, 9V blocks are common in multimeters, wireless microphones, guitar effects pedals, water leak detectors and older toys.

A four-pack suits a smoke alarm check: many homes have several detectors running on 9V blocks, and it is easiest to swap them all at once. Jot down the date you changed them, so the next time one starts chirping you know how long they lasted. The remaining blocks from the pack can go in the drawer as a spare for the next swap or for other 9V devices.

Worth knowing: these are single-use batteries and cannot be recharged. Many newer smoke alarms have a sealed ten-year lithium battery and don't take a 9V block at all – check the battery compartment before buying. Test each alarm with its test button after swapping. Don't store 9V blocks loose with metal objects, as the side-by-side terminals can short. Take spent batteries to a collection point.