Good battery, won't start

It sounds like you have a 12v drain on the battery while the car is off. Do you have the JBL sound system? There were some problems with the amplifier (I think) draining the battery. I believe it was corrected on a recall or TSB. Are you sure all interior lights are off when the doors are closed, especially the one in the cargo area? How much driving do you typically do? Are they all infrequent short trips?

If the battery was completely drained it is probably damaged and won't take a charge. Did you try to start the car with the charger or the booster battery attached?

 

Another thing to investigate is the connections. You can have a fully charged battery, but a poor connection. I haven't examined the terminals on the 12V or the block up front, but if I charged a battery and still had trouble getting a vehicle to start I would clean and check my terminals. I've had this issue on other vehicles so that I had to change out terminals or cable (or both), but in those cases it has been caused by the normal wet lead/acid battery causing some corrosion.

When you say it won't start, what specifically is happening? Is it that the ICE never fires or the car never reaches a ready state? Do accessories work?

 

A few questions:

• What was the method used to charge and test the 12V battery?
• Was the battery disconnected from the Prius when the charging took place? (the answer should be "yes", if more than a low charging current, such as 2A, was applied)
• Has a digital multimeter been used to measure battery voltage; if so what is the voltage when the car is IG-OFF?
• Have the mechanical integrity of the battery cables been verified (all hardware is tight, etc.)?

If the battery is indeed in good condition, but not even the headlights or dome lights work, then my guess is that the battery fuse (either 100A or 120A) has failed. This fuse is located in the little fuse block attached to the positive terminal of the battery.

However, if you find that this fuse indeed has failed, the next question is why did the fuse pop. Normally the fuse should not pop unless a serious electrical problem exists.

 

If the dome lights don't work, you should check the voltage up front at the jump start terminal in the fusebox and open a door to activate the dome lights. If you have a high resistance connection between the battery and the front terminal it will drop the voltage well below 12V when you open the door and the dome light will not go on. If the dome and other lights don't work the car won't start either. Tackle the simple part of the problem first.

 

I agree with the suggestion to check for voltage at the dedicated jump start terminal in the main relay/fuse box near the inverter. If the fuse located in the fuse block attached to the positive battery terminal is good, the next fuse to check is the 100A DC/DC fuse link. This is located in the main relay/fuse box. When you remove the cover of that box, note a plastic box around 5" long; the top is clear while the bottom is white. This box contains the large fuse links. I believe the headlight fuses are also in that box.

 

i read somewhere that there is at least a computer or two in the car connected to the dome light, and removing the dome light fuse is a method of rebooting parts of a prius.

 

Can you measure voltage at the dedicated jumpstart terminal?

If so, what voltage do you measure when the car is IG-OFF;
and what voltage do you measure after you unsuccessfully try to start the car?

 

Patrick, according to this person's post on PriusOnLine, this is the second 12v battery that only lasted 3 months. Something has to be draining the battery.

 

Hi Daisy,

Well, I'd expect that you should be able to measure ~12.6V from the dedicated jumpstart terminal to a ground point, when the car is IG-OFF. When the car is IG-ON (but not READY since the car won't start) then I would expect the voltage to be around 11+V.

If you don't measure any voltage at all, then that is evidence that a fuse has blown despite your efforts to inspect the fuses.

If you measure voltage, but much lower than cited above, then this is evidence that the battery is bad or that you have a bad connection to the battery.

Since you no longer have access to a meter, then if time is of the essence it would make sense to have your car towed to the local Toyota dealer for assistance.

 

Hi Daisy,

Well, did "someone" try to jump the battery?

The price of the repair is probably OK as it is not an easy job to replace the fusible link (this is the 5" long clear/white plastic box that I previously mentioned).

The implication of a blown fusible link is that the battery polarity of the jump cables was reversed and that the DC/DC converter in the inverter may be damaged. If so, then the inverter would have to be replaced at a price of ~$2K or so.

 

[another clueless post deleted. Sheesh.]

 

True, if the 12V auxiliary battery was shorted, then that would cause the fuse link to pop. However if the battery was shorted, then you would probably not have been successful in subsequently charging it.

If you find that the inverter was damaged, then this would be evidence that the jump polarity was reversed.