Surface pro 4 battery won’t charge completely with USB drive attached?

Has anyone experienced battery charging and battery draining issues with their Surface Pro 4?  (I know, that is a silly question, but humor me please).  I have had my Pro 4 for six months, and noticed that it takes more than 20 hours sometimes to fully charge the battery (even when it is turned off), sometimes the battery seems to drain while the surface is turned off, and the battery life seems to be much lower than the Microsoft state life expectancy (seems to only last 4-5 hours before it drops below 10%).  I took it to the Microsoft store last week and the tech there said everything seemed fine, although he said it was a little odd that the battery did drop one percent within a minute while he was inspecting it.  I have a Samsung 128GB USB 3.0 Flash Drive Fit drive in the USB port, so thought maybe the surface was expending battery power to power that drive.  After unplugging it, my surface was able to charge up to 100% without any problem.  Could having drives attached to the USB port of the surface draw battery power to the extent of preventing the surface from recharging its battery properly, and even drain the battery while in use quicker than normal?  I asked the tech this and he said it shouldn’t have that type of effect on the Surface.

I ran a battery report (which the tech read) and the “Current estimate of battery life based on all observed drains since OS install” shows 5:04 hours.  Seems short for only having had the surface for 6 months with only 22 recycles of the battery.  My battery info is below:

BATTERY 1
NAME
X910528
MANUFACTURER
DYN
SERIAL NUMBER
43332
CHEMISTRY
LION
DESIGN CAPACITY
38,152 mWh

FULL CHARGE CAPACITY
38,040 mWh
CYCLE COUNT
22

Any insight on the above would be greatly appreciated!