My car has low battery voltage

I'm considering buying a used car from an individual and during the maintenance inspection done by a YourMechanic professional, the only issue that came up was that he marked the battery volts as being "less than 12.5 volts". He also uploaded two photos that I feel are related…

The first showing a screen shot of his testing device's screen and contained the following info:

Starter Test
Charge Battery (in yellow text)
Crank Volt: 6.75V
Volt Percent: 38%
Crank Time: 644 ms

The second photo was this:

Charge Test
Normal (in green text)
Loads volt: 13.81 V
Loads off volt: 14

Experienced mechanics share their insights in answering this question :
Hello. From that test, I can determine that the charging system, as in the alternator, is fine. The voltage of the battery itself is very low, however. The starting volts are dropping way below the minimum, which means that the battery needs to be replaced. If you want to prevent the car from having any issues with the vehicle starting, I would replace the battery as soon as you have a chance.

If you are going to have the battery replaced, have one of YourMechanic’s certified mechanics come back out to you to replace it for your.

How to Identify and Fix Common car Problems ?

Our sources include academic articles, blog posts, and personal essays from experienced mechanics :

Regardless of which battery you choose, maintaining proper voltage (~12.6-12.8V for REDTOPs and ~13.0-13.2V for YELLOWTOPs) whenever possible will maximize battery performance and lifespan.
If you suspect your battery might have gone bad, measuring voltage is a good first step. If the battery is below 12.6 volts, you should attempt to charge it with a battery charger.
If your Toyota RAV4 battery warning light comes on while driving, be courageous to turn off your accessories, so the battery doesn`t drain further. The warning light usually means that the alternator isn`t working perfectly meaning you are operating absolutely on battery power.
Hybrid Vehicle (HV) Battery Pack and Auxiliary Battery

connected in series to produce approximately 244.8 Volts.

Check the Readings

Generally speaking, if your battery is over 12.45 volts, it`s sufficiently charged, and you are good to go.An ideal charge — basically 100% — comes in at 12.66 volts. If your reading comes in under 12.45 volts, retest your battery.

Car batteries naturally carry 12 to 13 volts unless you have a high-performance battery. Anything higher than 13 volts may indicate a faulty battery.
Yes, if your battery is underperforming it can cause systems within the vehicle to malfunction. A bad battery can also result in air conditioners, stereos and other applications not receiving enough power to function properly.
Faulty alternator, bad terminals, ground faults, bad cables are the main causes of low voltage output from the charging system to the battery of an automobile.
Under the hood, touch the negative terminal (black) with the negative meter probe (also black). Touch the positive terminal (red) with the positive meter probe (also red). Have a friend turn on the headlights and check the voltmeter reading. At 80℉, 12.5 volts or higher means your battery is fully charged.
Battery power drops sharply after that—a reading of 12.2 volts signals 50 percent power and 12 volts registers just 25 percent. If it reaches 11.9 volts, the battery is considered fully discharged.
RAV4 battery replacement could cost anywhere from $1,500 to $6,000, depending on which battery will be used, or nothing if you have an active warranty that`ll cover the replacement.
The ideal car battery voltage with the engine running is between 13.7 and 14.7V. With the engine off, you should get a reading of 12.6 volts. If the battery isn`t fully charged, it will diminish to 12.4V at 75%, 12V when it`s only operating at 25%, and down to 11.9V when it`s completely discharged.
What Voltage Should My 12v Battery Show? A fully charged 12 volt battery should read at 12.6 volts on the multimeter. If the reading is lower than this, you`ll want to charge your battery with either a battery charger or by taking your car for a drive.
For a car with a 12V engine, the normal value before starting is between 11.9V and 12.8V, and it should not exceed 14.8V after starting.
If the voltmeter reads between 14-15 volts then the battery is normal. But if the battery reads over 15 volts or less than 13 volts, then there might be a problem with the alternator. The alternator is over charging the battery or not giving enough charge to the battery.
12.65 volts or higher: Your battery is healthy and fully charged. 12.5 volts: Consider recharging your battery with a battery charger. 12.2 to 12.45 volts: Your battery is operating at 40% to 75% charge and should be replaced before it fails. 11.9 volts or lower: Your battery is considered dead and needs replacing.
A dead or low battery can be caused by a failing alternator. It can also result from additional draw from auxiliary lights, fuses, sound systems, alarms and such.
The same is true when measuring battery voltage to determine if a battery has gone bad. Fully-charged, most car batteries will measure at least 12.6 volts (~13.0-13.2V for OPTIMA YELLOWTOPs), but low voltage doesn`t necessarily equal a bad battery.
It`s not the voltage but rather the amperes or current of the battery to crank the engine. Use a multimeter or a DC volt meter for reading & it should be between 11.75V to 12.5V DC.
Have a friend start the car while you watch the voltage on the multimeter. It should drop no more than two volts while the engine cranks. If it drops any more or dips below 9.5 volts, you need a new battery.
A Bad ground decreases the supply of current necessary for the ignition coil to convert low-voltage/high current electricity in its primary coil into high-voltage/low-current power in the secondary windings.
The average Toyota RAV4 battery will last for about five to six years. However, this number can vary depending on how often the car is used, the type of battery, and the daily driving habits of the owner.
Car batteries can be tested at home or in an auto service shop with a multimeter. Or, if you fancy yourself a bit of a DIY mechanic, you can buy a multimeter online for about $10 and test your battery at home.

Relevant Questions and Answers :

the most relevant questions and answers related to your specific issue

When changing the car battery, do you "register" the battery to the car computer?
ANSWER : Hi there. Changing the battery has nothing to do with programming a battery. If the car was flat dead with a battery that lost all of the power because the dome light was on, then when jumped the vehicle will run fine. What may need programmed when the battery is replaced is the key fob. The key fob will lose programming to the computer as the vehicle computer is reset. However, if a 9 volt battery saver was put into a cigarette lighter and the car battery was removed, then the computer will not lose its memory and be just fine. If you need further assistance with your battery, then seek out a professional, such as one from Your Mechanic, to help you.

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Water was spilled in the trunk which soaked the car battery. Car won’t start now. Does water destroy a car battery?
ANSWER : Hi, thanks for writing in about the concern with the BMW 320i. If the battery was submerged in water then it’s completely possible for the battery to short out and die. Your friend will need to have the battery replaced. Also be sure to get all of the water out of the trunk. Have a certified technician, like one from YourMechanic, help you guys out if you need assistance with replacing the battery. Good luck.

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I have changed battery. I think I put non compatible battery initially and it’s start car alarm loud not turned off with remote ac
ANSWER : As long as the nominal voltage of the battery is 12 volts, it’s compatible. Of course, you need sufficient energy storage capacity, too, which in your case is probably around 850 cold cranking amps. As long as you did not reverse the positive and negative terminals (reverse polarity) when you installed the first battery, the battery is not incompatible. When new batteries are installed, inasmuch as any computer settings are lost, there can appear to be electrical problems, but such are not a fault of the battery. If, for example, you are having problems with the engine immobilizer system (security system) you may see a security warning light on the dash. If the warning light is on, to temporarily override the immobilizer system, see these instructions.

If you are experiencing electrical problems with other components, please simply request an electrical system diagnostic and the responding certified mechanic will get this taken care of for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

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My car will not start Intermittently. I purchased a new battery 2 weeks ago and yesterday the car wouldn’t start. Got a jump and
ANSWER : The issue you are having is probably due to an intermittent fault in the starter motor itself or a deficiency in the starter electrical circuit, for example a large voltage drop due to a poor ground or a high resistance connection. These issues can be readily diagnosed and resolved on a mobile basis if you request a hard starting diagnostic. If you request that diagnostic, the responding certified mechanic will get this resolved for you promptly. Based on Toyota’s Factory Service Manual, the battery should not be disconnected if the vehicle engine is running. The battery acts as a large resistive voltage sink and consequently taking the battery out of the circuit, while the alternator is still running, can create a voltage spike on the car’s electrical system which is not good for voltage sensitive components such as the engine computer. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

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2005 Chrysler 300C changed battery and alternator. Car started, ran, and then battery light came on. Shut car off and wouldn’t start.
ANSWER : Hi. There is a couple of things that could be wrong here. The battery or alternator that was just installed could be defective. Theses parts need to be tested for proper operation. There also could be a fuse, fusible link, or wiring for the battery or charging system that is blown or broken causing the battery light to come on.

The codes that you have will cause the car to shut down, run rough, or not start at all. The crankshaft sensor and camshaft sensor should be replaced. I suggest having a certified technician from YourMechanic come diagnose the charging system and check engine codes to help you proceed with correct repairs.

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Replaced alternator on car 2 times each time shows it’s charging 14v let car run for a little bit then test drive and car voltage
ANSWER : There are reports that the replacement alternators will not communicate with the engine computer and will not charge correctly. I recommend using only the manufacturer approved replacement part. It can be new or remanufactured but approved for use in the vehicle. Some lower cost alternators on the aftermarket will have charging problems since they will not communicate with the ECM on the vehicle and will stop charging.

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Battery and oil light come on when trying to start car, take keys out try again car starts no problem and lights go away
ANSWER : Of course, don’t switch gears without being fully stopped, unless your Owner’s Manual or the manufacturer has alternative advice. However, the gear shift issue has no relation to the no-start problem you are describing. Inasmuch as you only have 6,000 miles on the car, the "constant on and off" that you believe has occurred is meaningless in comparison to the expected total vehicle service life. That is, assume what you perceive as "constant on and off", during merely 6,000 miles, might be equivalent to using the car "normally" for three years. A new car should be trouble free for at least 5 years, unless there is a defect, so your "constant on and off" is not a causal factor for any fault on the vehicle. What you might have is a defect in the ignition switch, or perhaps the immobilizer system, but if the problem is not in the switch itself, clearly there is an electrical problem.

If your vehicle is under warranty, by law the dealer MUST repair the issue you are describing within a prescribed time frame and number of "attempts", otherwise the dealer will run afoul of Federal and state Lemon Laws that give you very specific rights, and recourse (contact an Attorney; we are Mechanics, NOT attorneys). Consequently, if the vehicle is still under warranty, to save yourself money do be sure to seek a resolution from the dealer. If the vehicle is not under warranty, obviously a certified Mechanic from YourMechanic could identify the electrical fault and resolve this for you. If you want to go that route, please simply request a no start diagnostic -electrical system and the responding certified mechanic will get this taken care of for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

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My car wouldn’t start after battery was just replaced my car cd player is running after I turn the car off
ANSWER : Your CD player definitely should not be running after the key is off and out of the car. It will certainly drain your battery. So the good news is you can be reasonably certain about what is killing your battery. I would remove any CD’s from the player and see if it still spins with the key out of the car. If you need to go a step further, you will need to disconnect the power wire to the stereo. It is located at the back of the stereo and this will require some dash disassembly to access the rear of the radio.

You will want to disconnect the stereo overnight to see if the battery dies. A quicker more accurate way of testing for a draw, which is what this is called, is to use an amp meter at the battery to confirm the stereo is the source of the draw. Most multimeters have amp settings that can be used up to a ten amp draw. You will need to connect the leads of the multimeter inline with the positive battery cable. Do not turn the key on while the multimeter is inline with the battery. The current will blow the fuse in the multimeter then you won’t be able to complete the test. Also, you will need to wait somewhere between ten minutes and an hour for all the modules in the car to go to sleep. Modules that are on will draw current until they go to sleep. You are looking for a draw of more than a half of an amp continuous.

With the multimeter connected, disconnect the radio connector and see if the draw goes away. You will see this reflected in the multimeter amperage reading. This draw test can be used to locate any draw that may be occurring. If you find the radio is not the culprit, you should then begin removing fused one at a time to see what is causing the draw. When the draw goes away after removing a fuse, something on that fused circuit is causing the draw.From there you will need to study a wiring diagram to see what is on that circuit.

Of course, all this takes an understanding of electricity to do these test. If you should need assistance with this, I recommend the following inspection; Battery is dead inspection from a certified technician from YourMechanic.

Good luck!

Read Full Q/A … : My car has low battery voltage