Battery drained for no apparent reason

I guess it's all to real if it happens to you. Like you I have never had the problem, but I usually drive 10 miles or more whenever I start the car. I think it could be a serious problem if it happens at a bad time. I made up a "jump start kit" with two high capacity lantern batteries, some wires with clips to connect them to the jump start terminal, and a note of which fuse disables the brake booster pump motor. If my battery goes dead unexpectedly I can be up and running again in a few minutes.

 

And out of curiosity, which fuse is that? I think I reasoned which one (or two) it would be once, but the manual isn't specific.

And have you tested that the lantern batteries actually have enough capacity with the battery disconnected, or are you saving that test for when you actually need them?

 

Yes I agree, the wiring diagram isn't real clear in that area but I am going to pull both F20 and F21. I plan to unhook the dead 12V battery, pull the two fuses, hook up my lantern batteries and start the car. Then I should be able to unhook my lantern batteries, hook up the 12V battery, replace the fuses and head on down the road. Well at least that's the plan.

Next time I have the 12V battery unhooked for something I'll try it, I hate to reset all my audio system buttons. I am pretty confident it will work because I think someone (can't find the post now) has done this with a gen2 and I think they used something smaller than a pair of lantern batteries.

If you decide to put a "kit" together get good quality lantern batteries, you can tell which are the good ones because they are heavier and cost more.

 

Prius 12 Volt Battery Drain

There continue to be postings about dead 12 volt batteries. Frequently, the OP states that no "lights" were left on. We must understand that the battery will run down in 24 to 48 hours if a door is not completely latched. It does not matter if the dome or rear hatch lights are off. Also, comments have been made about whether the car is locked or not relative to the 12 battery going dead. An unlocked car does not drain the 12 volt battery at a greater rate than a locked car. The parasitic current drain measurements that I have made indicate that the battery drain is minimal (about 0.020 amps) regardless of whether the car is locked or not. The only good thing that locking the car does is confirm that all doors are latched.

Lastly, you cannot expect the 12 volt battery to be recharged by simply driving the car for an hour. The charge acceptance rate for the 12 volt battery will be 3 or 4 amps. If you drive the car for an hour, you only charged the battery about 4 amp-hours. That is maybe 10 to 20% of its total capacity which is way short of a complete recharge. If you run the battery down, you must hook up a battery charger for at least an overnight recharge. Limit the recharge current to 3 or 4 amps (don't cook the battery).

 

I had similar problem today. I called road side assistance and scheduled them to come after I would be back home (date with Mom every Sunday at church).

I am glad I read this thoroughly since I thought driving around for an hour should have charged the car up. Hope my charger works...

Good news is the person that jumped the car had to read the manual as well as I. "We" figured it out together...

Now I know how to jump start the car...

 

This is a known behavior. And your translation is right on target. My understanding is that when a door (or hatch) is closed the car makes a check for the key fob being in the car (as a precaution against locking your keys in the car). When the hatch is not quite latched, going over a bump causes it to trigger a 'door closed' event.

 

A non-start due to battery issues in a 1 year old car (let alone a Toyota)

would be absolutely unacceptable to me.

How you have been convinced here that this is fine and possibly your fault is baffling.

 

Is it really baffling?

I am confident that 99%+ of people with this problem have left the lights on, or the doors open over night. Leave the lights on with any car and it will die over night. get over it.

 

You have every right to be mad about a 1 year new car not starting.

Every other car at that age can withstand a small overnight 5W drain and yet be able to start in the morning.

 

You are correct tp but I'm sure you know that the Prius has a smaller 12volt than most other cars since it is not needed to "start" the car.

 

you and your pals at GM should get the govt to recall Prius for too small battery.

 

The Prius 12V battery is smaller than others. Always locking the car will prevent the most common battery-draining situations.

 

+1

 

The small 12V makes it even more vital that one of the ECU's be programmed with enough smarts to shut off power draw after a period of inactivity. This is yet another of those negative things about the Prius which none of the "regulars" will tell you about.

A non-start in the early morning rush to work is the most annoying event. I have encountered it in the Accord but only after the 4-5 years of usage when the 12V is at end of life.

 

Trolling as always...

IIRC, I've left on a map light and/or interior lights on my 2nd gen Prius by accident at least once overnight and the car still started.

Yes, I've asked for the feature that Nissans have where the interior lights, including map lights are cut after 30 minutes at http://priuschat.com/forums/gen-ii-...es-other-cars-you-wish-2nd-gen-prius-had.html and many other threads. I believe power is cut to some lights on the Prius after a timeout, but not the map lights and/or not all the cases are covered. :/

I've never encountered a non-start situation w/my Prius. I did replace my 12 volt as a preventative measure a bit after 5 years.

 

That is what the spare vehicle is for.

I must be old-school, having learned as a youngster to not leave any lights on. My last battery-related nonstart in any car was in a handed-down Ford thirty years ago. Since then, all batteries gave enough warning to get replaced before failure, typically at 7 or 8 years.

Since being able to buy my own cars, my only non-start was due to an Accord fuel pump, at about age 15 (the car, not me). The spouse's Acura (i.e. Honda) suffered the same failure at a later age. Except for those, all the cars (including current Subaru and last Ford) gave enough warning of impending failure to get home, and get scheduled for repair, before reaching the stage of not starting.

The Toyota is much too young to be considered tested.

 

Did you disconnect SG at the OBD II port or at the tail end of the cable where the cable plugs into the SG unit? I have a suspicion my 12V goes down when I leave the SG connected overnight. So I was wondering if disconnecting just the unit from the cable will do or if I should disconnect at the OBD II port itself. I was trying to avoid the latter since that could cause damage to the port with daily plugging in and out. Thanks.