I just remembered, it doesn't freeze in Los Angles. Keep the old battery, just disconnect it from ground or put it on a battery minder. When you get back, reconnect the battery or disconnect the battery minder and drive off to air up the tires and see about ordinary maintenance. GOOD LUCK! Bob Wilson
I took the car to autozone, he tested the battery and he said it has a 12.5 charge, but it failed the load test. And sure enough, this morning it wouldn't start, even when it had been plugged in all night on a slow charger. It would only start when jumped. So...given all that should I get a new battery before storing it next month, for 9 months?
If you are not able to have anyone make the Prius READY for you for a 30 min period every month while you are gone (to keep the traction battery charged) then you should remove the 12V battery now and recycle it. Then buy a new 12V battery upon your return. If someone can help you make the car READY (not necessary to actually drive it anywhere) then replace the 12V battery now.