Had one where the battery clearly died… display just got more and more dim over about a week until finally it died. So I pried it open. It popped open quite easily and cleanly actually… looks like it had basically been glued down but in a way that it popped right open.
That’s all there is to them. It’s an 1130 battery, and the pen presses the metal tab down to make contact and start the timer. Somewhere in the circuit there is about a 5 second delay built in so that just a quick peek at how much insulin is in the pen won’t restart it.
Ordered some 1130s. Electrical tape holds the cap back together quite nicely