need battery update

At this time, there are no further updates to iOS 12.4.8 for the iPhone 6 that we know of. Only Apple would know!

For battery information and replacement options, if required: iPhone Battery and Performance - Apple Support & iPhone Battery Replacement - Official Apple Support

and for Touch ID fixes: If Touch ID isn't working on your iPhone or iPad - Apple Support

https://en.wikipedia.org/wiki/IPhone_6

iOS 12.4.8 is the last supported ios version for it and it's unlikely to be the last, unless they find some serious security issue

optimizing battery Batteries - Maximizing Performance - Apple

or you can get it replaced iPhone Battery Replacement - Official Apple Support

about touch ID then if it's not working it's likely a hardware issue rather than a software one

You need to replace your battery.