[One (M8) Q&A, Help & Troubleshooting] tsalta:
Hello Guys like me many of you have same problem with battery life, since i updete to MM my Battery start to droping very fast and suddenly die sometimes at 20% sometimes at 30% sometimes at lower %.

Something doing this we have lost all settings and after we boot the device again have to set up everything from scratch.

At the begining i was thinking my battery is DEAD and need a replacemant but in the past few months when i read hundred of Threads regarding this issue i realize it is not possible often after MM Update or flashed a MM ported ROM from HTC 10 this to heppans to so many users on the same time.

Ive tryed almost everything from fully Discharge to cleaning Caches Art etc and re flashing few times clean a new ROM nothing helps at all even some software for calibration make the things worse.

In this thread i found a solution given my HTC themself : http://xdaforums.com/htc-one-m8/help/phone-loses-settings-apps-battery-dies-t3375980

And i did try it several times without Luck

I did keep reading and found out that really Holding Volume UP + Volume Down and Power Button did clean the Battery Cache but i was doing it all the time wrong.

What i did try is this:

Turn off the Phone lets says you have 40 50 % battery left.

Wait for a minute or two, then Press and Hold Volume UP + Volume Down and Power button for at least 6 Restarts, release the buttons when your device swtich ON after this 6 restarts and see your Battery %, usually what gona heppand there will be diference in the reading. ( When doing this DO NOT PLUG YOUR DEVICE FOR REACHARGE)

in my case doing that before the operation i had about 46% after that i have 55% this is the 1st thing i spot on.

After i did this, start using my device with heavy use and i saw the battery behave normal and the droping its not so fast like before in order to chek do i have any more wrong readings i decide to prepare the test again.

Switched of the Phone at 40% after all the restars and turned it on i had 39%

so i think this was normal and the battery do not have anymore any wrong reading %.

Start to use hard the device watching videos listen music 1st think i notice is the % are droping really slow not like before.

At exactly 15% Battery left i recive a Warning like it should be!!! (i didn`t recive any warnings like this in the past few months) then i keep using it hard and waited the battery to drop even more to see whats gonna heppand.

Well at 5% all was perfectly fine NO restarting at all.

At 2% i put my device for reacharge and after the full recharge to 100% now seems the battery to HOLD really Good 24 hours latter with intensive use of the device the % are droping really slow like it should be.

Now its seems that all is fine.

Try this and report back.

Its important DO NOT PLUG THE DEVICE when you doing this! Its make SENSE even if from HTC says PLug it ON (DO NOT) because when you cleaning the Battery Caches you want it CLEAN not on the same time that power from the charger to reach your battery this can lead to wrong INFO again so its really make sense you have to do it without to Plug in order to see the real % you had.

Later on i will make some screen shoots to show you how the battery Hold after this procedure.

its seems now i lose 2% per 1 hour in standbay witch is PERFECT for old device.