mikieboyblue — You don't need to worry about the batteries during an absence of say 2-3 months provided all lights and accessories are left "off." The car sequentially powers down all its ECUs over a period of 2 weeks of disuse, so that it preserves its batteries' charge. The NiMH ("high-voltage" or "traction" battery) powers only the motor-generators (MGs) and the air-conditioning compressor, and can be charged only by the MGs, either from the ICE or through regenerative braking, and only if you are not in Neutral. The 12-volt battery powers everything else — lights, ECUs, gauges, sensors, door locks, power brakes, power steering, etc. It can be charged only by the NiMH battery, and only when the car is in READY mode. The ICE can be started only by MG1 from the NiMH battery. If the NiMH battery is too low to allow the ICE to be started by you, then Toyota can come round to your house with their Intelligent Tester. If it says that the NiMH battery still has enough charge to start the car without damaging itself, they can command it to do so, and you're on your way. The ICE will then recharge the NiMH battery, and thus also the 12-V battery. If the Intelligent Tester declares the NiMH battery too low for this over-ride, then the car has to be taken in for service. This should not normally ever occur. If the 12-V battery only is low (and the NiMH battery's charge is okay), you can jump start the vehicle as per the Owner's Manual. Just don't try charging the 12-V battery using anything other than a low-current (<5 amperes) trickle charger, or you may damage it, destroy it, or drastically reduce its life.

Stan