What is the voltage of a completely charged 18650 battery?
There are two voltages you have to think about. First is the voltage the charger uses this is almost always 4.2V.The other is the voltage the battery will rest at after you take it off the charger. ass son as you take it off the charger the voltage will drop until it settles at the resting voltage.Most chargers will leave 18650 cells will have a resting voltage 4.0V to 4.18V.4.00V-4.09 resting is a bit undercharged.4.10V–4.15V a correct charge.4.16V–4.20V is a bit overcharged.Undercharging will make the battery last for more cycles, overcharge will make it run long but reduce the cycle life.What voltage your battery ends up with depends on what current the charger decided to cut the charge at. the lower the cut off current the higher the resting voltage.
Can a battery have negative voltage? I have one showing potential as -0.03V on multimeter.
It's very possible and it happens when a battery is reverse charged. THis occurs when the battery is depleted but is in series with other batteries that are NOT fully depleted (although they may be close). It also requires circuitry that does NOT have low voltage cutoff (e.g.a flashlight or motor device - not an electronics device) In that case current continues to flow through the depleted battery until its voltage reaches zero. If the other cells continue to furnish current then the current is opposite the direction of normal charge of the depleted cell, and, in the absence of any charge to give up, the depleted battery is reverse charged. That can lead to a slightly negative voltage on the cell and is very bad for the cell, if continued it kills the cell pretty quickly - thus the reason most smart electronics have low battery cutoff and why, if you have a cordless drill, you should stop using it immediately when it slows down considerably instead of forcing it.The possibility of reverse charging is why you replace a battery pack as a group rather than individually, so that they all deplete simultaneously (the assumption that all the batteries manufactured in a group are nearly the same capacity).This is pretty much what Peter Hand is saying in his response.
My digital multimeter shows the actual voltage but the voltage keeps on increasing till I plug it in with the battery. What would be wrong with it?
If you're talking about reading on a DC millivolt scale with the leads open circuited, it's not unusual for the meter to pick up a slowly drifting reading because of its high impedance. But if it's doing it with the leads shorted together then it's broken.
Can we use mobile batteries for flying a Quadcopter?
No you can't!The reason being, quad copter motors, though running on medium voltages(6-12volts), consume huge amount of current, often in the ranges of (5-30Amperes). For comparison, my room has a 5 Ampere fuse. A Flying Speaker sound system for concerts, like this, consumes around 30Amperes (at higher voltages, like 220V).Your mobile phone battery cannot be used because:It's not capable of producing the voltage required by the motors.The current rating is around 2A. So it cannot power the motors. But surely, a combintation of enough number of batteries with load distributed so that each battery effectively supplies under 2A, the system will work.
How do you test a 1.5 v battery?
a simple digital voltmeter (DVM) will give a DC voltage reading of a least 1.35 volts butg ideally should be 1.5 volts. New high quality batteries read about 1.55 to 1.6 volts This does not show everything as it depends on teh load. The voltage reading may be good and yet still be bad as the voltage will drop under a load. It might work for a clock but not a for a toy with a motor- but the voltage test is accurate most fo the time
Are there any household items I can use to charge a car battery?
If you have a DC power supply that will provide greater than 12.6 volts, up to about 16 volts, then you can charge a car battery. You need over about 13.5 volts to fully charge it. Even as low as a 12 volt power supply will put something into a dead battery, maybe enough to get a car started. Hunt around for an old power supply, eg. from a computer or a printer. Connect the power supply positive to battery positive, and negative to negative.If you are really desperate you can use a portable power tool battery. If the voltage is up around 19 volts then I would just charge the car battery in short bursts, eg. 10 seconds at a time. Monitor the temperature of the tool battery by simply touching it. Pause to cool as necessary.If you have a voltmeter (or a multimeter) then use it to monitor to voltage across the battery terminals (with the power supply disconnected). A full discharged battery is 11.6 volts or below. A fully charged battery is 12.6 or above.If you are going to jury rig something then I strongly suggest that you disconnect the battery. If you accidentally apply a high voltage to the car you can destroy a lot of electrical components in an instant. There is very little risk to the battery itself if it is disconnected. It is pretty robust.
How is the battery percentage calculated?
The capacity of a battery relates to the time you can expect it to last and is measured in milliamp hours (mAh, i.e. electrical power the battery produces). The mAh you can expect to get from a fully charged battery is often marked on the battery label, but if it isn't on the label, then you can obtain it from the battery manufacturer's website. The mAh declines as the battery gets used, so by using a multimeter you can calculate your battery capacity.How to measure battery percentage (Basic using multimeter): Read the fully charged battery capacity on the battery label. For example, a lithium battery 2,400 mAh. Write down the battery's mAh.Turn on your multimeter and set it to measure mAh.Place the metal tab of the red wire from the meter to the positive terminal of your battery, i.e. "+". Place the sensor of the black wire to the negative terminal of your battery, i.e. "-".Read the meter display and write down the measurement. Use a calculator to divide the figure you wrote down from the meter by the figure from the battery label; then multiply the answer by 100 to get the percentage capacity in your battery. For example, if the meter reading is 600 mAh and the battery label is 2,400 mAh, 600 divided by 2,400, multiplied by 100, equals 25, so your battery capacity is 25 percent.If the battery is fully charged, it will be same as the figure you wrote down from the battery label (i.e. 100% ). If the battery is not fully charged, the measurement will be less than the battery label.More info: How to Calculate Battery Capacity | eHow
Is it possible to calculate how long a 1,000 mAh battery will last without knowing its output voltage?
It all depends on how you’re using the battery.The simplest case (that the other answers are alluding to) is when you connect the battery direct to a piece of equipment for which you know the current draw from the battery. Then just divide 1,000mAh by the current draw in mA and this tells you how long the battery will last in hours. In this case you don’t need to know the battery voltage. The reason for this is that 1,000mAh is actually a measure of the electrical charge stored by the battery, and current draw is rate of charge usage. Note however that at higher currents you will lose significant energy heating the battery and so you won’t get the full 1,000mAh.However if there is voltage conversion going on, which is always the case when the battery is in a USB power bank for example, then things aren’t so simple. If the equipment you’re powering draws 1Amp at 5V from the power bank USB socket for example, then you won’t get 1,000mAh from this socket. Power bank battery capacities are relative to nominal 3.7V Lithium cells, and so you get less mAh if you’re running kit at 5V. You have a conversion factor of [math]\frac{3.7}{5}[/math] to start with, giving you 740mAh, but you also have to take conversion efficiency into account. This is rarely stated, but 85% is a good working figure, giving you a final output mAh of 629mAh output from a 5V USB port. Further voltage conversions commonly occur in the device being charged.Of course modern power banks use variable voltage output technologies such as Quick Charge or USB PD, where calculations like the one above become useless. These are best dealt with by finding out the energy capacity of the battery, which you can get in Wh by multiplying battery mAh by battery voltage and dividing by 1,000. So a 3.7V 1,000mAh battery has an energy capacity of 3.7Wh for example. If you then know the power (rate of energy consumption) taken by the equipment being powered, you then divide the energy capacity by this power, also allowing for any conversion efficiency loss. For example 3.7Wh supplying a 2W output at 85% efficiency would last [math]\frac{3.7}{2}*0.85[/math] = 1.5 hours.