Are you asking about the 12V battery or the traction battery?
In my experience, owning a Clarity for 4 1/2 years, during which time the 12V battery was discharged on two occasions, I learned that a healthy 12V battery will hold a charge for 4-6 weeks, but not for 6 months. We never activated Hondalink or installed a dash cam or other device that could potentially add a load to the battery. In addition to having a Lithium jump pack onboard, I’d recommend using a battery maintainer if the vehicle is not expected to be operated for more than 4-6 weeks.
My experience with Lithium batteries, 2 PHEV’s, an RV and boat with a trolling motor, is that they will hold a charge for 2 years or more. The Clarity was left with a “fully”charged battery for 6 months. The battery gauge on the dash indicated no discharge over that time period. Likewise, the lithium batteries in the RV have been left to sit for similar periods with little to no discharge occurring. I use a Victron battery monitor on the RV. Interestingly, the battery manufacturer, Lion Energy, recommends fully charging the battery, after which it can be stored for up to 2 years. Other guidance is to charge a lithium battery to 40-60% SOC prior to long term storage.