M8 Battery and Settings issue after Marshmallow upgrade

[Hardcase19]

I am having an issue ever since upgrading my Verizon HTC One M8 to Marshmallow.
The phone will shutdown at around 20% battery remaining. It will not power back on.
Once I plug the charger in, as I did this morning, it shows 20% battery life and will now power back on.
This also leads to my notification settings and some app settings to be reset.
This is driving me nuts. I have tried clearing the cache multiple times and also attempted a battery reset, although not sure it worked, by holding down the power button and volume down I believe.
Is anyone else having these issues? Has anyone fixed it?
My last resort is going to be a factory reset but I really want to avoid this if possible.
thanks for reading..

 

[Stykthyn]

Mine does tthis as well. I'm told it's the battery software that tells the phone how much juice is left. There is a reset and I've done it but it doesn't work and I'm afraid that after 25 months my battery is on its way out.

 

[Hardcase19]

Is the battery reset you tried the one where you hold the power button and the down volume for 2 minutes?
I found and tried that one also, did nothing to help.
Also found a couple of people on other forums that are experiencing the exact same problem.
Never had the batter issues on KitKat but started immediately after upgrading to MM.

 

[Stykthyn]

Yes. It's been happening for about 8 months.well before the marshmallow update.

 

[Bleys1704]

I am having the same issue. While the battery dying at 20% is annoying the changing settings when I turn the phone back on is worse. It is driving me insane!
Dors anyone know why these settings are changing?

 

[Rukbat]

Lithium batteries don't last long if you deep discharge them. Anything under 40% is playing with fire. Constantly draining the battery to 20% will give you about 50% battery lifetime - or less.