If you can manage to order from the US Amazon, reliable third party batteries are $12.99 each: https://www.amazon.com/dp/B07284RX8X/

I don't quite understand. You are saying something like this https://www.amazon.com/ZeroLemon-LG-V20-BL-44e1F-Replacement/dp/B07284RX8X/ref=sr_1_4?ie=UTF8&qid=1512497140&sr=8-4&keywords=zerolemon+LG+v20 which is the standard size with the exact rating from the OEM battery, is giving you MORE battery life compare to the OEM battery the phone came with?

If so, how long have you been using the battery that came with the phone?