Happened to me too: 12v battery died.

Bummer! But aggh! ANOTHER battery thread to go with the other three?!

Just for that, I'm going to post my Optima page here too!
Prius Optima Aux

That'll teach you.

I did the Optima swap as a preemtive measure. To hopefully AVOID what others have gone through. We'll see if it works. I'm pretty surprised at the parasitic draw of the Prius. When you first shut it off, it is drawing almost 2 A still. That drops slowly, and after many mintues, I got tired of watching - my Ammeter showed still over 200 mA which is way too much at rest.

 

Paul,
Did you leave SKS on? That is the common cause for depleted battery and why they put an SKS switch below the Stearing wheel.

 

a lott off people have this problem
and yes i think its a design flaw.
i disabled the sks and stil got a drained battery
its just to small....

 

I'm having trouble figuring this one out. I don't measure any significant increase in current draw from the battery with SKS on or off. I'm going to keep trying though, because this car does some odd things when parked and seemingly doing "nothing."

 

Well, when you first shut off the car car there is the draw of the coolant transfer pump. Then, after a few hours, something else runs (manual is in the garage, too lazy to check what it is). After some time, the SKS will shut off on its' own. I think I read after two days of non-use, but someone else can check - it's in the owners manual.

While many speculate on what is causing this, I still maintain the charger built into the inverter doesn't have temp. compensation. Pearl runs the 12V system at 13.8 V both summer and winter. While 13.8 V is about right for summer, it isn't going to fully charge a lead acid battery when it's cold (around freezing temps and below). You need at least 14.3 V.

I haven't been caught yet, with a full week at -25C and below (went down to -35C on monday). Pearl sat for a few days at a time without being used. I do have my "Prius booster cable" in the "hidden drawer" in the console. You don't have to open the hatch. Boosting from the "boost point" on the fuse block works just fine, in fact, it's much safer than from the battery (NO chance of sparks igniting H2 gas).

 

Sorry to hear about the flat battery. Please boost the car using the underhood jump start point, far safer than monkeying around in the hatch.

I would make sure the 12 vdc is in fact fully charged. In cold weather, just driving around won't fully charge the auxilary battery, and you could damage it by keeping it chronically undercharged

I did post somewhere the genuine Toyota Prius PDI with very detailed instructions on how to properly charge the 12 vdc battery. Toyota is pretty strict about removing the battery first, which I thought was sissyness on their part

Another poster has commented he had a battery charger in the hatch area, and it got so hot it actually scorched the fabric. Lucky the entire car wasn't engulfed in flames.

Toyota recommends their own branded automatic battery charger set at 10 amp position. Their charger is a high quality automatic charger made by Associated. Any high quality automatic battery charger should work

 

Did you leave the parking lights on all night as you wrote you planned on doing?

 

nope

 

Fully charge the battery, and then have it load tested!

Icarus

 

Because it isn't a starter battery a load test shouldn't be done on it, unless the tech -KNOWS- what he/shes doing, and most don't when it comes to batteries. A load test on this battery should be at a much lower current draw. I've found if you leave the car off for 24 hrs or longer, and then measure the battery voltage, if you see 12V +or- about 0.5V then you're probably ok. You could then turn on the headlamps and see if it drops 2V. If so it needs to be replaced, as one cell is dead.

I recommend a "Battery Tender" if you plan on using a charger. www.Batterytender.com
It won't damage the battery, can be used with the battery in the vehicle, and comes with the cable you can install in the vehicle and just plug in (on the fuse block). I got the higher current version, though I haven't used it yet as my battery seems to be fine (knocking on wood). If you use the cable on the fuse block you open the hood to connect it, so it makes it harder to drive away with it connected.

 

As David Beale suggests, load testing properly. Any load test on any battery has to be done relative to the amp/hour capacity of the battery. I would question whether or not a ~2vdc drop with the headlights on indicates a dead cell. A 12 volt battery subjected to the load(s) of the lights (75-100 watts maybe?) would normally drop that much. The bigger question is does if recover when you turn the lights off, how fast and how much.

The ONLY way to accurately tell the voltage of a battery is after it has stood for at least an hour (preferably 12) with out being charged or discharged. That will give you an accurate voltage, but give little insight as to condition/capacity. The true an proper way to tell that is test the specific gravity of the acid with a temp compensated hydrometer. The problem is that you can't do that with a "sealed/maintence free" battery. The next best is a proper load test

If your service location doesn't know how to do it, perhaps you should fine one who can.

 

Any high quality automatic battery charger should work. A forum member almost had a fire in his Prius by leaving the battery charger inside the car. The battery charger got hot enough to scorch the fabric

If you feel comfortable doing so, it's probably best to just remove the battery and charge it up outside the car. You will lose your presets and have to "normalize" the auto window function, but you probably have to do that anyway due to the dead battery

The Prius PDI suggests this procedure to test the 12 vdc battery: turn headlights on for 60 secs, then turn off. Wait 60 secs. Measure voltage at battery. If 12.8 or higher, battery is ok. If not, fully charge and retest

Hope this works out. I'll be leaving for 2 weeks this Thursday, keep me informed