1 Get A Battery Swap
If all else fails, it may be time to take your iPhone into Apple for repairs or service. While there may be something wrong with the hardware of your device, it’s also perfectly possible that it just needs a new battery. iOS throttles devices with aging batteries to mitigate random shutdowns.
On newer versions of iOS, you actually have the option of enabling or disabling this feature (at the cost of increased random shutdowns). But, in general, getting a new battery will have a significant positive impact on your device’s performance. Through the end of 2018, they’re also significantly discounted.