(Now that I'm unbanned after 2.5 years, I can start posting again!) Long story short: Literally, the very first thing that I noticed after replacing my AT&T SIM with a T-Mobile SIM last June was that my battery would decrease at a much faster rate than when I was with AT&T. Generally speaking, I can use 1% every 2-3 minutes of basic cellular data usage (email, loading a few web pages, etc.). This is far worse than anything I'd ever experienced on AT&T. I've used 3 iPhone 5s and 3 iPhone 5ses, some jailbroken, some stock, some tested right out of the box, and cellular data battery life is essentially the same (see: pretty bad) across them all. It doesn't matter if I have a very strong signal or a poor one, it's all the same. Standby numbers are fine, and Wi-Fi numbers are excellent. Either the phone isn't optimized for T-Mobile, or this is just how T-Mobile (and other high-frequency carriers, maybe?) happens to be. Although, I had a Nexus 5 for a short while and the numbers weren't this bad, but of course that had a larger battery. Has anybody else noticed anything similar? I plan on getting an AT&T nano-SIM soon for testing and comparisons.