Phone constantly dying then turning back on?

So I have an iPhone 6s bought brand new about 3 years ago on Black Friday at my local Walmart. This problem only just occurred on Monday, January 24th. I wake up and go do what I need to in the morning. I'll be on my phone either scrolling on social media or texting. Then, everything will shut down and boot back up saying it is at the percentage that it dies at, once I enter my password however the battery drops immediately to 10%. Today it did this at least 3 times I'm looking into getting a new phone this weekend but if I don't have the money for it I'm stuck. Please, any insight on this issue would really help, thank you.