This just started happening today, but when I turn on low power mode, rather than the battery in the status bar turning yellow and displaying the battery % it just appears as an empty bar with no percentage next to it. Tried toggling the battery % on/off without low power mode on but it doesn't make a difference. Tried a reboot and soft reset but neither did anything. Not really a big enough deal to make me go through the trouble of restoring my phone... it's just annoying because it's a sign something is wrong. I'm on iOS 9.1 btw.