I just read interesting story about a guy who run down his 12V battery in Prius and then tried to jump it. To make long story short , it seems he reversed polarity and caused close to $6000 in damage which Toyota doesn't want to cover under warranty due to his fault of hooking up cables wrong, which he isn't even sure he did. Well, since our car is very similar to Prius I would advise anybody who has flat battery to be very, very careful with boosting the battery, since the inverter is right there and it's very expensive piece that could be easily damaged with reversed polarity (I even had brand new jump cables that were reversed with red clamp one side and black on the other of the same wire and it took me a while to figure it out why sparks were flying everywhere even after triple checking for proper connection). For the same reason I would suggest not to give boost to other people's car's either. The good news is our car doesn't need much, just to boot up computer, so probably even 12 v AA cell pack would be good enough to start it and using long, thin wires , not capable of large amperage hooked up to cigarette lighter should be safer, than jump cable with 600 amp capability directly to battery post.

I ran down my 12V battery once and after letting the car sit for a few hours, it was able to start whereas before, all attempts failed. I think the 12V battery might have charged up a little from the traction battery.

Otherwise, I would've gotten a car battery charger, disconnected the 12V battery from the car and trickle charged it. On page 294 of the manual, there's a special procedure for starting up after recharging the battery.

my friend has a honda civic hybrid and the same thing happened. The cables were hooked up backwards, due to unclear marking on the battery terminals and both batteries were drained. We jumped it again the proper way and it started back up. The battery charged itself up as he drove and nothing seemed to be out of order.

I dont know if the camry is different, but the civic certainly does not have this issue. this was the first generation civic hybrid too.

You can ruin the computer on any car when the polarity gets reversed, not only hybrids.

As for charging the 12V:
The good thing about the Toyo system (I don't know Honda's) is that it doesn't take much to start it (12V system). You could probably use your cell phone with the right connections.
The 12V battery is needed to start the computer & close up the relays to the traction battery, not much amperage needed for that. Once the relays are closed, the juice from the traction battery will start the car and charge the 12V battery.

After paying approx 30K for a brand new hybrid, one would think that the mfg would install a couple of $10 quality reverse polarity protection diodes...or fuse circuitry to the computers etc... What's wrong with these mfg's???

I don't know if TCH would have a problem with reverse polarity and I'm not willing to check, but I know some Prius owners had issues. I think inverter , the one that charges 12V battery from traction battery uses Mosfet transistors and those will get damage with reverse polarity. The amount of computers and electronics inside TCH is much larger than in any normal car and those are very sensitive to any abuse. Even if the system is protected from reverse polarity with diodes, who says protective diode can not fail? Fully discharged battery will recover some of the voltage after it's left alone, which may be just enough to start the car after a while, but with the car in off position I don't believe there is any charge coming from traction battery, there is a relay that physically disconnects it from the rest of the system and it needs 12 V battery to energize and let recharging begin.

Why bother to jump a Prius or TCH with another car.
All you need is enough amps to close the inverter relay and boot the computer.
A 12 volt flashlight (two 6 volt lantern batteries) will do it.
I carry a 12 folt emergency power source that can recharge via the 12 volt auxilary outlet (aka cigarette lighter).
This assumes your traction battery is not dead. If it is no jump will get it going. A dealer needs to charge that battery.

My TCH 12V battery died a couple of weeks ago. I triple checked the polarity on the cables, which were connected to my Honda Odyssey. I didn't even need to start the Odyssey. On accident, I pushed the button to start the TCH before starting the van, and it started right up.

I can understand why one would only need some flashlight batteries to get this car going again.

The current drain from the 12-volt battery is ~10 amperes when the vehicle is ON but not READY. No small flashlight battery can supply such current. As soon as the vehicle comes READY, the NiMH battery can start recharging the 12-V battery, but not before. The reason for the high current drain is that all the basic electronics (display, all the ECUs, etc.) are powered from the 12-V battery. See my measurements in the thread "Disconnecting the 12-v battery."

Stan

Both D and Lantern batteries would have no problem producing 10 amps for an hour. I suspect even the smaller ones could do it for the few seconds it takes to boot the computer and close the inverter contactor.

http://www.techlib.com/reference/batteries.html