What you need, my friend is the portable power bank. They usually have a gigantic 10 - 50,000mAh batteries so your phone can basically last forever with them
Also the prices are ridiculously low for such a useful device. They range from $20 - $50 and they come in all sorts of shapes and colors, so you can match them with your phone and also use them as an accessory aesthetic improvement device
Anker PowerCore Speed 20000
Anker PowerCore II 10,000 Slim
RavPower PowerStation Series 20100mAh
DXPower Armor DX0001
All of these listed are top notch and some of the highest quality and lowest price, look them up and choose for yourself, you can't go wrong with these 4.