12 volt battery drain after 3 weeks non use- normal?

Hello,
After 3 weeks or so of non use, 12 volt battery does not have enough juice to start car....use cables to another battery start it. It is a relatively new battery ..is this normal.??
How long can your car sit without using before 12 volt is drained? Thanks in advance!

 

Thanks for all this input- much appreciated! Yes, this is a 2016, not my 2004. Some background: this car may suffer from too little driving. I got it from my dad, who occasionally drove it. He had the same problem, dead 12 volt. My guess at that time was that he put the car in park, and after pressing park button, assumed he had pressed on/off button... and left car on. (easy to do!) But I really did not know. Since his battery was 5 years old, he decided to have the dealer put in a new one just in case. So.....the current one is about 2 years old . To be clear, this car spends life being parked much of the time. 24k miles on a 2016 tells the story. So.....on a 2 year old battery, 3 weeks idle draining it seems a bit questionable (?) So, wondering if I forgot to 'turn car off' (assuming that would be a cause). I'll look into a 'battery tender' thanks! ...............For the record, I miss the gen 2. Perfect amount of tech imo. Currently, lots of little bells whistles that are supposed to add convenience adding 5 inches to the owners manual. ::end rant::

 

Doug McC : re seldom read document (aka 'war & peace')....good point. Just not have had a chance to peruse. Pages on end of frivolous bells and whistles minutia repels...
Fuelmiser: re leaving it in park-power on. I knew this applied to my 2004....just spaced it out. I have an inverter hooked up to 12 volt in 2004....can cook, etc while parked. Toyota should build these into prius. Fascinating feature. I think I could have cooked a roast beef dinner in an instapot hooked up to inverter while driving (?).....park for night leave car 'on' to maintain constant temp if needed. If DougMcC is right and it shuts down after 30 minutes...then this would not longer work.
Mendel: gonna get a "battery tender jr' -thanks for tip!
Why I miss my 2004:- Despite its faults (wheel bearings, brake actuator, steering -!! mine disconnected while driving! sued toyota , but lost), oh, little leak high on back hatch that rots out battery well, and corresponding area on right side- my battery was dangling over road held on by cables!!) 2004 is a tank! just right amoutn of tech. (no 2016, I dont need cutesy video of car driving everytime I start up!) , glove box-2016 useless...way down low hard to access. 2004 perfect. 2016 Headlights: modern harsh white blue lights impossible to change bulb. Sure, save some deer, but blind oncoming drivers. end rant.
DougMcC : like your Einstein quote. This one has been on my mind lately:

"A world federal government with powers adequate to guarantee security is not a remote ideal for the distant future. It is an urgent necessity if our civilization is to survive."
"Only by transferring military power to a supranational body, which derives its moral and legal authority from the fact that it genuinely represents individual member nations, will peace be secured. Peace cannot be achieved by gradual development, peace requires a decisive radical step..." ~ Albert Einstein

Thanks for all this advice!