How to quickly update the zImage of my phone

Hi
I am building different versions of zImage, and I need to be able to flash the phone with it so I can test my software. My question is what is the best and fastest way to do this please? Currently I only have USB2 on my workstation, so as far as I know fastboot is not an option. What I do now is to pack the zImage into a boot.img and tar that with other files from the stockrom and flash the whole thing with Odin. My requirements are:
1- I need to have the phone rooted; so for now I have to root the phone after every flash
2- I want nothing else to change but the zImage
3- I like to keep everything else the same; i.e. my personal data, text messages, call logs, etc.
I am going to USB3 capability very soon.

New Huawei g play mini phone drains battery very quickly

Here is a screenshot of my battery drain

Is it normal , or should I go to service center ? My previous phone had much less sloppier curve . When I bought the phone I charged it upto 100% and then started using it , though at the shop they told me to charge for 3 hours. Is it because of this ?