Originally Posted by
MStieb
Does anyone know of reliable and cost conscious battery replacement service? I don't want to sell a phone with a bad battery.
I'd check the battery settings panel to make sure there isn't an unexpected app draining power. If you do upgrade to iOS 11.3, it will show also show your phone's battery health. Alternatively, there are some third parties apps.
Regardless, the cheapest replacement options is probably actually Apple: $29 through the end of the year.