12v system question

Hi Brin. The Prius uses it's drive motor/generators (MG1 and MG2), which are an integral part of the transmission, to to charge the traction battery. And it uses a DC-DC converter (electronics) to step down this battery's 200 volts to provide power to the 12 volt system. So there is no separate generator/alternator, and power for the 12V system comes indirectly from the Prius main electric drive motor/generators.

 

There is a very good method to test the health of the 12V system shown under the "DO-IT-YOURSELF TEST PROCEDURE" here: Weird stuff happening? MPGs dropping? Test The Battery | PriusChat

 

First of all, it's its not it's.

Now that that's out of the way.

Get a cheap android phone, a cheap ELM327 bluetooth OBDII adapter, and the Torque app for android and then you will able to monitor lots of stuff (rpm, engine coolant temp, and aux battery voltage) with your phone as you drive. You check the stand alone aux battery voltage after taking the Prius out of READY mode. If you check it in READY mode the aux battery will read 14 volts because the DC/DC converter is charging it - akin to an alternator charging the battery in a conventional car.

 

LOL, I've always wanted to type the sentence: It’s not it’s it’s its.

 

So is the 12v battery charged only when mg1 or mg2 are running? Or is it charged thru the dc-dc converter when the hybrid system is in READY mode? I have an 06 and just paid for a third battery. The first lasted 6 yrs, which is good. The second battery lasted less than 2 years. Other cars have an alternator which charges the 12v battery just fine as long as the battery is maintained. Dont tell me I have to manually charge the 12v battery every night or even every week.

 

The 12V battery is charged via the DC/DC converter whenever the Prius is READY.

What was the brand of the second battery that you had purchased?

If you log fewer than 10K miles per year you may need to apply a supplemental charge to the 12V battery 2x per month unless you are content to replace the battery relatively frequently.

 

With a seldom-driven 07 (about 2,000 miles/year), the deep-cycle Optima Yellow Top has been working well, without any supplemental charging. Prius booting is a great application for a deep cycle battery, and their service life tends to be longer than the original starting-style battery. Optima has a direct-fit product for the 2nd-gen (DS46B24R). I used to have to do some supplemental charging with the original battery.

 

Both batteries were Toyota parts. I have heard of bad 12v batteries in other threads. The second battery was installed at a Toyota dealership.

 

I drive my car to work, about 15 miles but 30 minutes (Los Angeles traffic) one way. I just want to make sure the 12v battery is getting charged. The remote key thing is off (button under steering wheel) so that the 12v battery does not discharge too much. We take an occasional trip (Los Angeles to San Diego), and it was during one of these trips that the original battery died. The second battery was bad at the 100k inspection.

 

The OEM Prius battery is a deep cycle AGM battery and not a starting style (flooded lead acid). It has the same chemistry as the Optima.
The difference is that the Optima has spiral wound plates against the traditional flat plates. This means the Optima has lower capacity than the OEM because of it's waste of space between the circular cells when they are put next to each other. It is reputed to be more reliable than the OEM, but this is beginning to be bought into doubt by the many reported batteries being delivered discharged or faulty.

John (Britprius)

 

That sounds good. Next question: how many 'deep cycles' can the oem battery take before damage is done? Sorry for all the questions, I am trying to save $$.

 

The OEM battery does not appear to stand up well to being deep cycled. This may be because the Prius has virtually no current limit when charging the battery from a low state. However on the top of the battery it states maximum charge rate 4.5 amps. The Prius can easily charge at a rate of more than 10x that figure. This does not stop many owners getting many years of service from them.
The upside is that the new Toyota Truestart OEM battery has come down in price and has a long prorated Guarantee. Another good choice with a long full replacement guarantee is the Exide Edge battery FP-AGM51-JIS direct fit battery.

John (Britprius)

 

So the car cant properly charge its own 12v battery, but it sure can charge the traction battery???

 

Shoot, I messed it up again. Mine came with a flooded 12v battery but I didn't realize that the AGMs in most of them were deep-cycle, stock. Thanks for the info. The YellowTops are working out much better than the original style in the 2006 and two 2007s in the extended family.

If your GS battery happens to be flooded as well (remove top sticker, clear plastic insert and little rubber vent plugs, look inside and see if there's water instead of gauze mats), mine benefited from some additional distilled water--the level was below the top of the plates--and a day on the float-charger. If it's not a flooded type, don't add water.

 

So the 12v battery may be able to be serviced? The dealer told me that the 12v battery (at least mine, anyway) was a gel-celled battery and couldn't be serviced except to replace it. But that was the dealer...
Don't get me wrong, I love my car. Got ar '14 Prius for my wife. Just need to save $$$ more now.

 

At minimum, you can fully-charge the 12V battery using a charger intended for AGM batteries, set to 4A current output, and see if that helps.

If the battery does not hold a charge, you can remove the top label of the battery (upon which is printed a warning not to remove the label), then remove the translucent plastic cover over the six cells, remove the individual caps over each cell, and look inside. If the cells have a fuzzy white mat between the lead plates, then the battery is AGM. You can try adding 1-2 ounces of distilled water to each cell but do not fill the cells with water. This may give you some added service life.

If you see that the cells contain liquid acid and regular lead plates, then you can try filling the cells with distilled water as needed.

That is it, for service.