Q: Since last iOs update when my iPhone has between 20% - 30% charge it just turns off and I cannot turn it back on until I charge it, once I plug it it goes back on and shows more than 20% charge. Is there a solution to this?

Welcome to Apple Support Communities, patolem!

I've got to say, great job of locating the troubleshooting steps concerning your iPhone 6 on iOS 10.0.2 having problems with charging. I'll be glad to help but you and your friend.

If your iPhone, iPad, or iPod touch won‘t charge -- Since you've tried all of the troubleshooting available for you with this issue, step 6 is the answer.

6. If your device still won’t power on or charge, take your device, charging cable, and charging adapter to an Apple Retail Store or Apple Authorized Service Provider for evaluation. You can also contact Apple Support. 

Be sure you have a back up of your iPhone ( How to back up your iPhone, iPad, and iPod touch ) and be sure to turn off ( Set up Find My iPhone, iPad, Apple Watch, and Mac -- Turn it off instead of on ) before you go.

Take care!