Default [Q] Need help with several HTC One Dual Sim problems

So, a month ago I bought a Russian Htc One Dual Sim. Works almost perfectly, except some little problems...

1. Battery drops instantly
2. Audio latency

1) so, when my One reaches about 30% battery it starts dropping instantly several times till its off. For instance today it was 32% when I took and saw it drop to 25% in a moment. Then followed 25->19->15->8->5->4...0
This happens every time when it reaches 30, sometimes 20 percent battery. On an unrelated note, the main battery drainer is the Android OS or Kernel, 20% or less when using heavily and up to 95% when idle.

2) the audio latency is another issue which was present in android 4.2.2 and has become EVEN WORSE in 4.4.2. So when I'm playing games or the drums the sound comes almost a second after I've tappef the screen (the latency was less than half a second in 4.2.2) I tried turning off Beats and it helped veery little, but the quality got a lil' worse as you might expect.
Still I cant find any solutions for these problems.

By the way, I am on a non-rooted, S-on android 4.4.2/sense 5.5 phone. My blinkfeed, autosync and similar battery eating apps and services are off. Waiting for responses!
Thanks in advance,

Vahe.