Help iphone 5c keeps crashing

so recently i have been having a problem with my iphone 5c it keep crashing and turning itself off. It can be a complete pain to turn back on and sometimes i have to do a complete restore. At first i thought it might be an issue with the battery as it seemed to happen only when i had around 60 to 75 percent charge on my battery but on the occasion when i get the phone to turn back on after its crashed it has stayed on until the battery is on about 30 percent. I updated my phone to the newest version of ios about a week ago and since then the crashes have become a lot more frequent. So does anyone have any idea why this is happening and how i could fix it.