I have an old truck that has a current leak some where and rather than try and find it I just installed a kill switch on the battery. If the Clarity is prone to have the 12 volt battery discharge if left sitting for 2 week (or less) should you disconnect the battery before leaving it? Will this cause any damage?
Some people have experienced that the 12V battery on their Clarity died after a week or two of the car not being used. Others have gone much longer with no problem. It's possible that the ones that died the 12V battery was already weak.
Putting a battery tender on as already mentioned is generally the best method. Battery Tender is actually a brand, probably the most popular one, but there are others.
Removing the negative cable from the 12V is okay also, although it will reset your history so your estimated EV range will be off for the first few drives while it builds history back up. Also whenever the 12V is disconnected, the next time you start the car there will be all kinds of ominous warning messages about ABS and several others, this is normal and those messages will clear within the first mile of driving.
Another option, if you will have access to the car and just won't be driving it, you can turn the car on to READY mode for about an hour every few days, this will charge the 12V battery.
Another option is to do nothing and just be ready to give it a jump start if needed. Although if it requires a jump start then probably the 12V is weak, and draining it down will accelerate its eventual demise. But I guess maybe that's one way to test the condition of the 12V battery by seeing if it will survive two weeks without charging! As a side note, the portable jump start batteries work quite well especially on hybrids as hybrids don't need a lot of power to start, the lithium portable jump start batteries are small enough to fit in the glove box.