A strip of plastic means you have to have a spring at that end of the battery, a hole in the device for the plastic strip, and enough structure around the battery to hold the spring and battery separately. The hole also makes waterproofing more difficult.
All of this would add weight and size, and those trackers are really small and really lightweight. Judging by the photos, the battery is just hard wired to the circuit, and the whole thing is encapsulated with a thin layer of epoxy for waterproofing. That's by far the cheapest, easiest, and most reliable way to build something as lightweight as possible.
I doubt they use a socket that would allow the battery to be isolated, it's probably directly soldered in for weight and reliability. Otherwise they could just ship the battery uninstalled and let the user plug it in when he gets it. A weight of 0.15g doesn't give a lot of room for extra components like a battery socket.
Perhaps they could put a tiny antifuse in circuit with the battery inside the IC package. Supply external "programming" current to the IC, and it would melt the antifuse and get the battery going.
The whole device is encapsulated for waterproofing so supplying any current at all to it is tricky.
It says it's light activated. So likely they've put a tiny light sensor in it that the microcontroller polls occasionally during the lowest power mode. That might be a tiny solar panel too. But using that to electrically drive an electronic power switch is tricky if you don't have the budget for a custom ASIC; if you don't have that budget, you'll add a decent amount of weight in a device that tiny.
Honestly, I'm not at all surprised that they've chosen to accept a short shelf life instead. It's pretty remarkable that they can squeeze that much functionality into a 11mm long by 3.5mm diameter cylinder.
I would think that the engineers developing then already did the cost benefit analysis and decided that shipping them activated (and tested) is the best option for their users
Or just bring one of the battery leads out of the encapsulation and cut it. Just a tiny bit of solder and you hook it back up. With the rest of the device waterproofed just one tiny exposed contact should still remain waterproof with thin gauge solid conductor wire. There's no voltage differential so it shouldn't rust moreso than just a regular blob of solder exposed to the elements.
I wonder why its not just two interconnecting cylinders (using a tiny gasket) that you push together with thumb/finger when you want to activate/power the device.
Given that there would have been some serious engineering to think through the design there must have been trade-offs that I'm not considering though.
That'd probably be a good solution if the transmitter didn't need weatherproofing. I suppose adhesive film could be placed over the gap after removing the tab, though.
