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.
With the motor running, the multimeter rating should stay in the 14 to 14.5 volt range. Dropping below 14 means either the battery is weak and unreliable for sustained vehicle operation or the alternator is failing.
A good alternator should maintain battery voltage between 13.9 and 14.8 volts (14.2 is optimum). Even worst-case, with all accessories turned on, there should be at least 13 volts at the battery.
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.
If your battery has a charge between 12.4V and 12.7V, your battery is fully charged and ready to run. If your voltage is below 12.2V, it needs to be recharged. Take a 30-minute drive on the highway or pick up a charger to bring the voltage back up. If your voltage is higher than 12.9V, the battery is overcharged.
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-volt batteries supply useful energy only through a limited range — from over 14 volts (when fully charged and unrested) down to 10.5 volts in use/under load (when lights dim, pumps groan and TV pictures get small). No 12-volt battery will remain at over 14 volts for more than seconds unless it's being charged.
14.4 volts is the gassing threshold. The battery above will slightly gas, but not enough to be harmful, and the battery will get a quick full charge recovery after starting. 14.8 would start to be a worry (there might be liquid or corrosion on the battery) and 15 volts would be a real concern, but 14.6 is fine.
14.1V means the alternator is charging the battery.
If the measured value is 14.4V DC, it indicates that alternator is working perfectly and there is no problem in it. 14.4V DC is standard or normal voltage of an alternator while car engine is running.
Measuring your car battery's voltage can help you determine how charged your battery is. A perfect voltage with the engine running is between 13.7 and 14.7V. With the engine off, it should be 12.6 volts.
14.5-14.6 is normal voltage while the alternator is running.
A fully charged car battery should be between 13.7 and 14.7 volts while you're driving. One way to test your battery's power is by starting the engine and turning the headlights on. If the headlights are dimmer than usual, this could be a sign of a poorly charged battery.
When the vehicle is started, without the introduction of a load (the lights or air conditioner), the volts will usually rise to an average of 14 volts. If the multimeter reads at more than 14.8 volts, then this can be considered as overcharging.
Amp/hour Capacity
In this case, the 14 indicates that a fully charged battery of this size will light a bulb that uses exactly one ampere for 14 hours until it is considered dead (an actual voltage reading of 10.5 volts is considered a dead 12 volt battery).
12.0 volts or below - At 12.0 volts your battery is considered to be fully discharged or 'flat' and should be recharged as soon as possible. The lifespan of your battery will be severely affected if it remains within this voltage range for extended periods of time.
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.
A fully charged battery should register at 12.7 volts or more. If the voltage falls below this number, the battery should be recharged. A battery is only charged by one quarter at just 12 volts. Once it drops to 11.9 volts, your battery is considered dead.
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.
When we take a closer look, we see car battery voltage can range anywhere from 12.6 to 14.4. With the engine off, the fully charged car battery voltage will measure 12.6 volts. This is known as “resting voltage.” When the engine is running, battery voltage will typically rise to 13.5 to 14.5 volts.
At 12.4 volts the battery is considered 75% charged and can still ignite your engine. When the battery voltage lowers to 12.2 volts without the engine running, it is considered a bad battery that may start your engine but is no longer capable of holding a charge.
Now if you were to short this or draw high current using a low value load it could cause a fire, but electrocution, no. Can a 14v DC get someone electrocuted? Dry skin has a high resistance, and 14 V with a small contact area is not much of a threat.
AGM batteries are designed to require 14.6v – 14.8v when performing a full charge from a state of discharge, whereas standard lead acid batteries need 13.8v – 14.4v, hence this is what most onboard chargers are designed to deliver – not the 14.6v – 14.8v that AGM requires.
So, to answer your question, Yes, 15 volts is too high. Most car alternators, that normally recharge your battery after every start, and provide power while the engine is running, are normally voltage regulated to about 13.8 to 14.0 volts.
Yes, assuming it's a regulated voltage supply (most are).