12V Battery

90% the battery is bad. I would take it to another auto supply for verification.

It should last three weeks when new, maybe two weeks at mid life. It really should not need a battery maintainer for three days off time.

If you are electrically proficient you could run a parasitic draw test. Should not be drawing more than 30 ma after 15 minutes with all lights off.

I would do the auto supply load test first.

 

Sounds like Batteries Plus owes you a replacement battery. You may want to bring it back to them…

 

The CCA tests the capacity of the battery (kind of like will a gallon jug actually hold a gallon). So it shows your battery is only capable of producing slightly more than half of what it should. The test your dealership should do is considerably more accurate than an auto parts store or even the battery store.

 

CCA (cold cranking amps) is not directly a measure of capacity. It's a measure of instantaneous power. How hard will it crank that 12V starter motor in your antique gas powered car. It takes very little power to start a Prius since the 12V doesn't turn an old fashioned starter motor.

But it does need to hold a charge. If it's not holding a charge (amp hours), then it won't have much power available for the CCA test. So it's still a relevant test, but not a primary rating in a buying decision. Amp hours is more important for a Prius.

After a drive from LA to SD and back, that battery should have been fully charged, so it sounds like it's not holding the charge. I'd bite the bullet and get the Toyota battery with the 84 month warranty. It should last you quite a few years. It's all I put in my Prii.

 

For those interested in learning more I refer you to article BU-806 at batteryuniversity.com. Or you can go to that site and search for CCA.

 

That is, take it back to another Auto Parts Store, and have them do a free load test. Do be sure it is fully charged before you take it there.

 

You just go there and they do it free

 

Yes. You could just buy a battery based on the dealer test. Remember you could have an excessive parasitic draw as well.

 

Toyota’s battery comes with a very good warranty and, in addition, IF it is dealer installed, the first two years it is 100% replacement.

 

The testers as far as I know will force you to charge prior to running a test. Sometimes you would need to leave the battery with them so they can charge after which the tester will run a test. I have not seen any tester run a test on a discharged/not fully charged battery, some combo units will just start charging…

 

charge the battery and check the voltage, then check again in the morning.

then repeat with the neg cable disconnected. otherwise, you're flying in the dark and at someones mercy

 

An old school full cycle test charges, discharges and charges again. Can take hours. A rapid cycle test allows today's load testers with computer cycling and monitors to calculate capacity in minutes even on a partially discharged battery.

A battery used to drive the car to the test location will have enough charge since the hybrid system can quick charge any battery well over 12v / 75% in a few minutes. A good battery would Ready the car two weeks later. Does not mean a bad battery or one with excessive parasitic draw will stay charged three days later.

Again there is either a bad battery based on the dealer and that is causing a three day discharge unable to Ready a Prius (typically less than 10.5v) AND OR an excessive parasitic draw (three days at 250 ma or more - typically the rear hatch light or an aftermarket device or a scanner in the obd2). Normal parasitic / constant off state draw should be 25 ma or less.

 

Actually the dealer test is rather reliable. The only real question is if parasitic draw killed the battery. For the paranoids who believe the dealer would lie about the load test, I recommend another free test.

 

what you are saying here is not wrong, for a battery that is not deeply discharged. (say, below 12v for AGM)
Even at 12.5v, it can take hours to fully charge a lead-acid battery - with a 4 amp external charger.

There are not many vehicle systems that have a DC-DC charger (if any). The DC-DC converter in the Prius system supplies a steady 14 volts (nominal). If that fully charged a battery, it would not be long before it started over-charging, as it never stops while On.

If you want an accurate load test, fully charge any vehicle battery with external battery charger first. For the Prius, it should be a 2 amp or 4 amp AGM smart charger. A 2 Amp charger would take less than twice as long as a 4 A.

 

Not trying to start an argument or anything but what is your basis for this advice (regarding disconnection of the negative cane)? First time I’ve heard of that being necessary.

 

that will tell you if it's the car or the battery

 

rjparker is absolutely correct concerning the new rapid testers. There’s no need to put a battery through a complete cycle to determine capacity (you can, and yes it would), but there is no need when today’s testers can accurately (at least reasonably so) determine Internal Resistance which is going to give a good indication of capacity (and the ability of the battery to deliver said CCA). The dealership’s test has already shown the battery is shot. Change it already and have them check for excessive draw.