Voltage drop question

What is your battery voltage when the car has been setting for a few hours? I dont think the voltage matters when the car is turned on because what your seeing is the charge voltage. I think mine stays around 13.4v when the car is on. I dont think I noticed it fluctuate while driving but I will try to watch it on my way to work tomorrow.

 

If the ON voltage is fluctuating there may be a problem with the 12V regulator, or an intermittant short. I'd start by disconnecting all aftermarket stuff (for example, the amp) and see whether the fluctuations go away.

 

The battery voltage seems quite low. You've charged the battery for 10 hours plus your commute time, but that may not be sufficient charging time.

1. If you have access to a battery charger, I'd suggest that you disconnect the battery from the car and charge the battery.

2. Do you have access to a digital multimeter? If yes, then I'd suggest that you measure voltage at the battery terminals when the car is IG-OFF and after several hours have elapsed to dissipate surface charge. Then measure voltage when the car is READY.

3. The DC/DC converter is supposed to maintain voltage on the 12VDC bus at ~13.8VDC when the Prius is READY. There is a voltage sense line connected to the battery's positive terminal via a 5A fuse. If the DC/DC converter senses that the 12V battery is unusually discharged then it can adjust the voltage to some extent.

4. Have you been noticing these wide voltage fluctuations even with your aftermarket stereo equipment disconnected?

5. Sometimes a voltage fluctuation is due to a loose connection which introduces a varying level of resistance into the circuit. Have you checked the battery terminal connections to ensure that they are tight? On the negative side you need to check the terminal connection at the battery as well as the connection to the body.

 

Well I watched my voltage on my way to work today it it stayed at 13.4v. Only a few times did it changed to 13.3v or 13.5v and only for a second.

My battery is normally drained most of the time since it does not get a good charge. It sits at about 11.5v at rest most of the time.

I would say as long as your not getting any error codes and your battery is OK you should not worry about it. The voltage is still within acceptable range.

 

That behavior does not sound right. You may want to contact the manufacturer's customer service department and explain your issue to them.

 

I agree. Either the charger or the battery is not working properly.

Assuming that the charger is working, then a discharged battery (in otherwise good condition) should take substantial time to charge. That demonstrates that it has lots of capacity. Maybe the battery has prematurely failed?

Regarding the negative battery cable connection to the body, I recall that jayman reported corrosion at that point so his practice is to periodically remove the hardware, clean the corrosion, lubricate, and then reassemble. I haven't noticed a problem with my 2004 in that area.

 

Sounds like the battery has developed a high impedance. A charged battery with no load should be 12.6 volts. I suspect your battery has prematurely failed.

 

Hi F8L, I’m sorry to hear you’re having trouble and I’d like to help. If your battery has been discharged to the point where it needs a jump, it’s a good idea to fully recharge the battery with a battery charger as soon as possible. I realize this isn’t always practical, but relying on an alternator to recharge a deeply-discharged battery can lead to a cycle of dead batteries and jump-starts until either the battery or alternator fails.

The voltage your ScanGauge gives you when your vehicle is running is the output of your alternator and should read between approximately 13.7 and 14.7 volts when your vehicle is running (TheForce, you may want to have your alternator checked).

If you have checked your grounds and they look solid, you might want to check for a high “key-off†load. A typical key-off load is about 25 milliamps and you may need to wait up to 15 minutes for some of the computers in your vehicle to go into sleep mode.

We have videos on YouTube that offer tips on proper battery charging as well as techniques for testing for current draw and how to determine if your battery needs replacing. Unfortunately, I'm not allowed to post those links, but our YouTube account is "OptimaBatteries."

Please keep us posted on your findings!

Jim McIlvaine
eCare Manager, OPTIMA Batteries, Inc.

 

F8L - There are 3 simple tests that will give a good indication of the health of your battery.

1) Does the battery charge to a good voltage? When new, a YellowTop will charge to about 13.2v, if charged using a an appropriate (deep cycle) battery charger. If charged using a regular automotive battery charger it would probably be 12.8v. In most cars, it wouldn't be unusual for this to be as low as 12.6v. Although this isn't applicable in your specific situation, if any battery is discharged below 10.5 volts, many standard battery chargers will not be able to recharge the battery. We have a video on YouTube (OptimaBatteries) that explains a parallel charging technique for charging these deeply-discharged batteries with a standard charger, although I am currently not allowed to post links on this board.

2) After charging, does the battery hold voltage properly? Right after your drive your car, or charge your battery, the voltage you read will be of the surface charge, and will not be of the true voltage of the battery. If you wait 24-48 hours, the surface charge will dissipate, and you will measure the true voltage of the battery (see above). If you were to leave your battery disconnected for another day, week, even a month, the voltage should not be significantly different (maybe 0.1-0.2v less). An Optima battery has a lower self discharge rate than most other batteries.

3) After charging, does the battery deliver power how it should? If your battery has passed tests 1 & 2 above, take it to almost any auto parts store or battery specialist, and ask that they do a load test. This test isn't something that really can be done any other way, but fortunately, most places will perform this test for free. It is critical that the battery has been charged properly before doing a load test. If you have a battery that is too weak to start your car, and an auto parts store gives you a charge and test result in a few minutes, the test result is suspect.

If there is a problem with your battery, please call your original retailer for warranty service. He will be able to walk you through the process for getting the battery back to him and processing your warranty transaction. If you have any other questions, please don't hesitate to ask!

Jim McIlvaine
eCare Manager, OPTIMA Batteries, Inc.