Normally all the GPS trackers due to their size limitations are made with small batteries that can’t power a GPS tracker 24/7, since you have to power plenty of modules (like Wi-Fi, Bluetooth, cellular communications, etc). This is of course different in the case of pure Bluetooth trackers, thanks to Bluetooth Low Power (short BLE) trackers with this technology can last for years. However, you have to remember that those purely support Bluetooth which means the device will work in a limited range of usually 10 - 50m and you can’t point to the exact location with it. While it is cool for things like a wallet and keys tracker, it might not be the best way to track your pet, bike, kid, etc.
I hope that answers your question “Why do some trackers last years and some just a few days?”. Now let’s come back to trackers that have more than just Bluetooth on board. Different technologies like Wi-Fi, cellular modems, and GNSS receivers aren’t that low power compared to Bluetooth, which is why all the GPS trackers came to the idea of cycle loops.
Summing up the purpose of data loops is power-saving, while still delivering relevant info. That is why all PRO trackers try to predict, measure and calculate when your device is going to sleep or transmit its location. The better they are set up, the longer they will last on a single charge.
So what are the cycle loops? Well, simply described, since you can’t run a GPS tracker constantly on an integrated battery, you need to do some sort of delays, and those delays are those magical cycle loops we are talking about. As easy as it sounds it is way more complex. If you just set a delay with a constant not changing “sleep time” you would save up some battery, but it is just a start. Just imagine how cool it would be if your device would sleep as much as it is not needed or moving! This is the moment where different sensors come into the game, like the accelerometer, as it can always tell you whether your device is moving or not. Adding that up to a “sleep time” we can get quite a powerful power saving.