Most likely a jump start will get it started, either with booster cables or with one of those paperback-sized portable jump start batteries, which actually work really well especially on hybrids because cars like Clarity the 12V battery is used only to get the electrical system running and then the much larger HV battery takes over.
Once the car is on (make sure READY appears on the display) then the HV battery will immediately begin charging the 12V. Unlike a gasoline car where you would then need to drive the car for an hour or so to get the battery charged, with the Clarity you can just leave it sitting in the garage turned on (again make sure it says READY) and it will just sit there quietly charging the 12V battery. Of course check to make sure that your EV range is above 0. I'm not sure how long it takes to fully charge the 12V from fully depleted, but I would think leaving the car on in READY mode for at least thirty minutes will give it enough of a charge so that it will start the car without a jump, assuming that the next place you drive it to will be the dealer. If however you plan on first taking it to the grocery store or wherever then I would let it sit in READY mode for at least an hour to try and get the 12V more fully charged. And even then you will want to bring a portable jump start battery with you since the overall condition of the 12V battery is unknown at this time. But to be even safer the next trip should be straight to the dealer. Assuming that it jump starts there is no real need to have it towed to the dealer unless you just feel more comfortable doing that, especially if they do it for free under roadside assistance.
The dealer can check for codes to determine if there are any other underlying problems but assuming you are able to jump start it then the odds are that this was simply a case of a less than fully healthy 12V battery that drained after two weeks of sitting. The dealer will hopefully replace the battery for free under warranty as two weeks of sitting is a bit too short of a time period for a 12V battery to fully deplete especially for a car that is new. Unless there were any add-on accessories like a dash cam that were draining it. That being said a dead 12V battery after the car sits for two weeks is not unusual for Clarity, but not because the batteries are necessarily inferior but because many of our cars sat for a long time on dealer lots without being charged, which shortens the life of the battery.
Hopefully the dealer will replace the battery for free under warranty but that's up to them to decide. If they won't do it under warranty and you are hesitant to buy a new battery at this time, especially at dealer prices, then at least go to an auto parts store and have them test the 12V battery. If they say it needs replacement then at least their price will likely be a bit less than the dealer. If however you aren't that concerned about the cost then it will certainly be easier to just have the dealer replace it while you are there. Either way I wouldn't recommend going too much longer with this battery because once a 12V battery has been fully depleted even just once its days are numbered. Some might last another year or so after just one full depletion, but this battery already has exhibited that it's probably somewhat worn out, and again this may not be the first time it was fully depleted, no way to really know. We're coming into warmer weather now so it might make it through the summer but the risk goes up if you try and take this battery through next winter. Some people have reported that their Clarity can get fussy when the 12V battery is not working right so that's why it's probably better to just bite the bullet and plan to get a new battery now instead of trying to drag this one out any longer. Obviously if the dealer will replace it for free that becomes a moot point.
Looking ahead to when your car is back in the garage with a new battery, you will want to maintain the health of your new battery if the car will continue to sit for long periods. You can get a battery maintainer, which are a modern and much better version of the old trickle chargers. A popular brand is Battery Tender. Some people just leave the maintainer plugged in all the time as they have circuits to prevent overcharging, but it's safer to just use the maintainer every few days, i.e. connect the maintainer until it indicates that the 12V is fully charged then disconnect the maintainer. Alternatively you can simply turn on the car for about thirty minutes every few days or once a week or whatever (again make sure it says READY). Note that just having the EVSE charger plugged in won't by itself keep the 12V battery charged, as it only charges the 12V while it is charging the HV battery. And even then the charge rate for the 12V battery is much lower than when the car is in READY mode.
Last edited by 2002; 04-25-2020 at 01:35 PM.