Hello,
Since I am new to this I was hoping i can get some info regarding the issue Im having.
I started recently having issues with my 1989 k100.
First it was with the battery loosing power. I charged it and it worked fine. After couple of days riding it started loosing power and the bike would stop while riding. Took it to a mechanic and it seemed that the battery totally lost power, as soon as i would connect jump cables the bike would start and work fine.
Today it happened the same thing while i was riding i noticed the engine wasnt sounding right and soon enough it stopped and it wouldnt start up. I used the jump cables again and it worked fine.
Im starting to believe that the bike is draining the battery somehow or maybe just the battery is gone bad. 
Anyone had the same issues or is just me....
Any feedback is appreciated 
Thank you in advance

Is the battery fairly new and fresh, or has it been through a few seasons and likely to be on it's last legs?

A fresh battery at 100% state of charge should read 12.7 vdc or higher with no loads pulling current, aka open circuit voltage or OCV.  If it is reading 12.0 or lower OCV then it is at about 45% state of charge.  There are tables on the internet, so measure you battery voltage and determine it's state of charge.  Then try to charge it and see if it holds a charge.  A weak, old, or worn out battery can't hold a charge anymore, and that is likely your problem.

Take the battery to an auto parts store and ask them to load test it. It's free. (Because it helps them sell new batteries.)

THANK YOU ALL...

Suggest you check the 'Kill' switch for intermittent operation.
(Corrosion in my K75 Kill switch will prevent starting occasionally and will also cause the engine to cut out suddenly.)
I have found that if I pull the end of the switch backward it will stop killing the bike, so I have a wad of paper behind the end of the switch.

From the sound of things your battery is okay, what may not be working is the charging system.  After the battery is charged it's all good, after some riding the bike konks out.

Put a volt meter across the battery and start the engine.  One the engine is running and revved up to 3000 RPM the voltage should rise up read at least 13.2 volts, preferably closer to 13.8, if it goes up any higher than 14.5 volts you have a problem, overcharging, although this won't cause the bike to quit.  My guess is that you'll see the voltage drop after the engine has been started and not come back up.  The wheels stop when the voltage gets below 11.5 volts on an old K bike.

Once up and running the bike gets just about all it's power from the charging system, if that's not working your range will be quite limited.

- John