I have a Prius electrical theory question. Assume these facts: 1. DIY 12v cigarette lighter outlet wired directly to 12v battery (fused, of course) 2. Car in READY mode Question: Given those facts, would plugging a load into DIY cigarette lighter socket be any different than plugging the load into the OEM cigarette lighter socket? I'm guessing "no" since the 12v battery charges from the DC to DC inverter..
When I tap something off "at the battery", what I really do is tap off with a ring terminal on the bolt at the car/cable end of the main fuse link that's built into the positive battery post clamp. I still add a smaller fuse appropriate to whatever size wiring I am adding, but this way, the main fuse link limits the maximum overcurrent that my smaller added fuse could need to successfully break.
The OEM cigarette lighter outlet has a 10 Amp fuse and is tapped after the Ignition, so it does not drain the tiny battery when the Prius is 'off'. If you are using less than 1/2 Amp, you might be safe using a direct connection per ChapmanF, but I bet you occasionally drain the battery.
In real life, my aux-power thingy includes an off-the-shelf gizmo called VCM-06, which turns the power on and off according the system voltage it senses.
