What can I do to improve my iPhone battery health?
My phone’s battery health capacity is 86percent is low, what can I do to make it 100 percent
[Re-Titled by Moderator]
There's no way to increase the maximum capacity % on an almost exhausted battery.
And be careful (start making a backup of your iPhone on a regular basis), since your battery is reaching the critical point of its life, and could have unpredictable behaviors. I suggest that you have your battery replaced.
Regards
Giulio