opening a stuck battery cover on the Polar Wearlink transmitter

The battery cover of a Polar Wearlink+ transmitter (T31) is intended to be opened by turning the slot with a suitably-sized coin. Considerable force is required to rotate the cover, but the cover is made of soft plastic and its shallow slot is easily sheared by the coin edge. After the slot is damaged, the coin will slip when turned. So far, I have already ruined two covers.

 Battery cover









 Polar Wearlink+ transmitter and soft-strap (textile electrode)






On a website lamenting about the same problem, a commenter suggested drilling two holes on the cover and using long-nose (needle-nose) pliers to turn the cover. However no detail is provided.

Here's my iteration of the aforementioned suggestion. First, I drilled two 1.5 mm blind holes on opposite sides of the cover. I chose the hole diameter to fit the tips of long-nose pliers that I own. To prevent water ingress, the holes are supposed to penetrate only part of the cover's thickness; i.e. blind holes. But the cover is only 2 mm thick and it is hard to control the depth of the drilling. Anyway, if by accident, a hole penetrates the cover completely, it can be plugged with silicone glue.

two 1.5 mm holes drilled into the top and bottom of the battery cover

More Mizunos with fragile uppers

Previously, I have blogged about the Mizuno's uppers being prone to tearing. The Mizuno Wave Impetus (photos below) has this problem too. Below are different coloured variants of the same model. The red shoe is in worse shape than the blue one because the former has been worn longer. Again there is still plenty of life left in the outsole despite the torn mesh.

An attempt to patch the hole. Sew a piece of cloth over the hole but can't tell how long will this hold up.