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Scion xB Battery Problem

Hi All,

I’m having a problem with my 2005 Scion xB. A 1-year old battery died on me in January, and the problem was diagnosed as the alternator overcharging the battery. I replaced both the alternator and the battery, but two months later, the new battery has died. The battery appears to get a normal current from the alternator at this point. I have replaced the battery, but I expect that this new one might die if I don’t get a next opinion. The first garage was unable to diagnose the problem.



With batteries, there is a difference between “dying” and “going dead”…Sometimes batteries are discharged by a hidden load somewhere in the car which results in a “dead” battery…There is nothing wrong with the battery itself (or the alternator) you just have to find what is causing the discharge and eliminate it.

A simple test called a “Parasitic Load test” will quickly find the problem…

I’ll try this when I get home. However, the last two times the battery has been inoperable, it didn’t maintain charge when it was jumped and would die as I drove it down the street. What would this indicate?

If the car is dieing while you drive it after a jump, then you have an alternator issue. The Battery is strictly a storage device, it stores energy. This Energy is mostly to power the starter when you go to start the car. THAT IS ALL IT DOES… After the motor is running the power is supplied by the alternator, So if you can fire off the car on a jump start and it dies shortly after… It’s an alternator issue (connection, improper install, or just a defective part)

I agree with @gsragtop Under the conditions you describe, the “BATT/ALT” warning light should be on…

Today, “rebuilt” alternators are not very reliable…Have it tested…The best way is off the car…

Your vehicle doesn’t have an alternator but instead has a generator. The voltage regulation to the battery is controlled thru the ECU or the computer. Here’s a wiring diagram of your charging system.

The computer may have failed where it’s no longer allowing the battery to be charged from the generator. However, the computer in your vehicle is covered under the manufacturer warranty for 8 years/80,000 miles. So if the computer is the problem, and you fall within the warranty period the computer should be replaced by dealer for free.


Knock me over with a feather, I would have never guessed a 2005 car would have a generator. The last car I had with one was a 1956 Studebaker
Tester- are there any other late model cars running around with generators?

Yes.There are a lot of newer vehicles that utilize generators where the voltage is controlled by the ECU instead of an alternator. There’s two reasons for this. First, generators are cheaper. But most importantly with a DC generator there’s no chance for AC ripple voltage from a failed rectifier from an alternator to confuse/damage the sensitive computers/modules in todays vehicles.

I know of a lot of people who’ve tried replacing the battery/generator (thinking it’s an alternator) trying to figure out why the battery won’t charge. When all the long it’s a faulty ECU that’s preventing the battery from charging.


oldtimer 11"Knock me over with a feather, I would have never guessed a 2005 car would have a generator."
It doesn't. What is mislabeled as "GENERATOR" in the Scion wiring diagram is just your common, garden-variety, three-phase, internally rectified, ALTERNATOR.

Alternator? Where’s the rectifier bridge and diode reflected in the wiring diagram? If it were an alternator the wiring diagram would look like this.


The diode rectifiers are internal to the alternator and are not shown in the wiring diagram.

Google scion alternator and you will find a list of auto parts stores who are selling them.


It is an alternator, pure and simple, with six internal diodes and slip rings (and NOT with a commutator and brushes).

I have been avoiding saying so before (because I am such a nice person), but in this case:


It would appear that you’re not keeping up with the technology being used on todays vehicles.

Here’s the instructions on how to mount the GENERATOR from GM for a 2005 Chevy Cobalt.


You are still dead wrong. The pic you provided is an alternator, not a generator, regardless of the name someone applied to it. Do you know the difference between a generator and an alternator? Fundamentally, they are very different devices, and they look quite dissimilar.

We need an emoticon for <throwing up hands in exasperation>. I’m out of here. But you are wrong, wrong, wrong in calling that device a generator.

I don’t call it a generator unless it’s a generator. Gee? I wonder if GM knows the difference between a generator and an alternator?


Generator is the the SAE J1930 term for alternator. Today they are both the same device.

The terms are interchangable. I have to agree with Mechaniker on this one. There are a lot of components inside the alternator not normally shown on a drawing, along with a lot of other things in a car. The ECU for instance. They just show a block with lines tied to it. Those things are normally treated as the least replaceable part. Even though the three phase diode ring isn’t shown in the drawing you can bet it is inside the “generator”.

Lost in semantics imho. A generator produces dc current, an alternator produces ac current. An alternator has a rectifier to turn the ac current into dc current, the end output for the both is the same, 14.5 dc voltage. They are 2 different approaches to get to the same result. If the belt that turns the mechanism and the mechanism puts out dc current it is a generator. If the Mechanism puts out alternating current it is an alternator.

An alternator puts out DC with a slight ripple.