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Some apps stop running in the background if you move them from Phone memory to Internal SD card. Settings--Apps--All--UC browser--Move to internal storage. Also, try unchecking options like 'Send anonymous usage data' or 'UI improvement program' in UC browser. Try these, and if they don't work, check if you have added UC browser to exceptions list in Stamina mode. Settings--Power management--Stamina mode. If nothing works, you will have to only unistall the app and install another browser.
I am not sure, because on my phone Android OS uses typically less than 5% of battery. May you have Google calendar sync, Google contacts sync, etc. on. Or may be it is because of some other app running in the background, which makes Android OS use battery, like task killers or some sync services. Of 1d 19h of total time on battery, Android OS has used CPU for just 15m on my phone.