12 volt battery drain? or Converter Charging??

Did you test the Optima battery before installing it? There have been several posts on Optima batteries having low SOC on delivery and needing to be charged before installing.

 

I would suggest to use a voltmeter on the 12V system to monitor what the voltage is when the car is ready. Although there are several threads about entering maintenance mode to read the 12V system, it has been pointed out that this is not necessarily so accurate, just a rough indication. Also, a DC clamp type meter can monitor the charge/discharge current on the 12V line to the battery, so that would be a way to detect unusual drain.

You should see ~14V or so if the car is successfully charging the battery. You would not expect to see much of a drop in that voltage if you turn on the headlights. You would expect to see just small milliamperes of current drain in the off state. A cheap clamp volt/amp meter from Radioshack should be in every DIY tool box, IMHO.

Otherwise, getting set up with a mini VCI would allow you to check these things from the OBDII port.

 

Optima strikes again.... Compared to every other non-hybrid car the Prius puts so little load on 12 volt batteries that crap battery makers like Optima can corner the market... Optima Jim himself openly admits right here that they re-sell faulty batteries:

"many of the “bad” batteries returned to us under warranty now are actually just deeply-discharged and work fine, when properly-recharged. In fact, I have a workbench full of "dead" Optimas that we refer to as “adOptimas,” because we find new homes for them after we recharge them, rather than just sending them off to the smelter.

Read more: http://priuschat.com/threads/trickle-charger-and-12-volt-battery.123826/#ixzz2kyvrrkMF
Follow us: @PriusChat on Twitter | PriusChat on Facebook

 

repeat post due to PriusChat admin fail...

 

repeat post due to PriusChat admin fail...

 

Steve,

12.01 volts is basically a 50% SOC for a AGM battery. The Prius charging system is wimpy in my opinion. It will keep a battery charged as long as the car is driven regularly and if the battery is not severely discharged. I have heard and read different outputs or charging rates concerning the charging system on the Prius. My opinion is as long as the voltage is 13.8 to 14.2 when in "Ready Mode" measured at the jump post under the hood then the charging system is working.

If the Optima you bought won't hold a charge of at least 12.6 volts, I would return it and ask for a new one that is fully charged.

It is a good idea to check the voltage at the posts with a digital volt meter before you purchase a new battery. A fully charged AGM should measure a minimum of 12.8 volts. Just because someone sold you a new battery does not always mean it is fully charged. A lot of times, that new battery has set on a shelf and discharged. Once that happens, sulfation has already began to set in.

 

1. You are not allowing sufficient time for the 12V battery to be fully-charged. 4 hours is not enough. It would be better to charge the battery overnight, then look at the battery voltage after the battery has rested another day to dissipate surface charge.

2. The Prius DC/DC converter operates at ~13.8V which results in a relatively low charging rate.

3. Although you have driven the car daily for 5 days, how long is the car driven each day? It doesn't matter whether the headlights are on or off because the DC/DC converter regulates the 12V bus voltage at ~13.8V.

 

I have done a fair amount of testing on the Prius (gen2) charging system, and it is capable of charging at higher voltages than 13.8v. I have recorded 14.6 volts actual (not MFD reading) at currents of over 50 amps. I agree with Patrick that 4 hours charging "unless your charging at 10 amps" is not enough, and if the charger is shutting down after this short time the charger faulty, or the battery is sulfated and has low capacity.

John (Britprius)

 

Hi Steve, the obvious thing that you need to do here is to use your voltmeter to take some readings of the battery voltage (which is also the dc-dc converter voltage) when the Prius is in ready mode.

It should read about 13.8 to 14.0 volts in ready mode. Some people notice it reads a little higher (around 14.1 to 14.3) soon after first making it ready, but it usually drops back a little after a minute or two. If this ready state voltage is verified directly at the battery terminals then there is no reason why it shouldn't be keeping the batteries charged.

Once you can verify that the ready state voltage is correct, then we start looking for either a faulty battery or a parasitic load problem.

BTW. There is a state where the ready voltage can drop to around 13.3 to 13.4 volts, but only under certain conditions and only after it's been running for 30 minutes or so. Don't worry about this right now, just make sure that you're somewhere about 14.0 soon after starting.

 

Steve,
It looks to me that your car has a leak or short somewhere in +12V circuitry that discharges the battery when car is turned off. Are you sure NONE of the interior or door lights are ON when you leave the car? The way to check for parasitic leak would be to measure the CURRENT through the battery with Ampere-meter when the car is off (don't forget to turn off the light in the trunk as your gate will be open )

Just my 0.02
- Alex

 

I'm having a similar issue in my 2008 Prius. I purchased an Optima YellowTop from elearnaid about 18 months ago and I have to charge it every single night with my CTEK charger. Even after a full charge the voltage is low. I did a parasitic draw test with everything off and did notice something on the "dome" fuse pulling more than anything else in the car (almost half an amp). I did not jimmy the hatch latch when testing, but did turn off all the dome lights.

Even when driving around with the "dome" fuse unplugged for a week (and a full charge from my CTEK), I still have to charge the Optima battery every couple of nights. I drive the Prius 6 days a week at least 30 minutes a day. I'm thinking I have a bad battery, but don't want to replace it only to find out something is draining it.

Did you figure out what was causing your issue? Anyone have any suggestions? My 2008 Prius is the base model without the smart key.

 

There is a relay that can stick and cause this problem. It has been discussed on the forum in the past. I will see if I can do a search to locate the posts.

John (Britprius)

 

Steve are you using a charger for an AGM battery. An ordiary car battery charger will not reach the required voltage to charge an AGM battery. This needs to be 14.6 to 14.8 volts depending on temperature.

John (Britpius)

 

High Daniel. When the doors or hatch are opened the Prius boots some of the ECUs in preparation for starting. This is probably the 1/2 amp you're seeing. If you keep the doors and hatch closed for about 5 minutes (it's ok to still have the hood open) then you should hear a relay click and the current suddenly drops to a much smaller amount. If you aren't seeing this then there migh be a stuck relay problem as BritPrius said. (BTW. If you have the smart key system then keep the key fob well out of range when testing this).

Can you elaborate a bit on that Daniel. Do you have to charge it in order to achieve some perceived required voltage, or does it actually fail to boot the Prius after a number of days if you don't do so?

 

I appreciate the quick responses. I will run another test with all the doors/hatch shut ASAP. I do not have the smart key system so that won't be a concern .

The issue does prevent the Prius from starting. Sometimes I can get it to start, but the red triangle comes on. As soon as I fully charge it, everything starts normally. I don't recall exactly what the voltage is fully charged, but it was around 12v. The next morning it is usually between 10.5 - 11.3v. I've been having the issue for the past month and haven't changed anything in the car since the last 12v battery replacement.

 

A fully charged Optima off load should be a minimum of 13 volts. I am afraid this sounds like another faulty Optima battery unless something on the car is discharging it. Leaving the battery disconnected over night and checking the voltage would soon prove one way or the other.

John (Britprius)

 

Charged the battery to full this evening. It was on the charger for about 6 hours and now reads 12.63 volts. I've disconnected the battery and will test in the morning.