iPhone turning off on 10 - 20% and battery percentage not showing right I have an iPhone 5s running iOS 11.0.3. When it's down to about 15%, it dies completely.Can I do something about that?

Also, when It's at around 15% and I plug the iPhone into the power supply, it often goes up to 25% instantly.Why is my iPhone doing that?
I agree with Tyson, these are classic "dead battery" symptoms. If you want to be certain before ordering a replacement battery or having it repaired, use a battery utility, such as coconutBattery (for Mac) or 3uTools (for Windows). It will tell you what the health of the battery is (Design Capacity). If your battery shows anything less than 70% of design capacity, it will require replacement.