The basics of charging any battery
Most batteries charge the same way: you connect them to a power source using the correct cable or charger, and the electrical current flows into the battery until it is full. The time this takes depends on the battery size, the charger strength, and how empty the battery was to start. A phone battery might take 30 minutes to two hours. A car battery might take several hours or overnight. A laptop battery usually takes one to three hours.
The key is using the right charger for the device. A charger made for one type of battery can damage or fail to charge another type. Phone chargers, laptop chargers, and car battery chargers all work differently because the batteries themselves are different sizes and chemistries. Using the wrong one wastes your time and risks damaging the battery.
Key Takeaways
- Always use the charger that came with your device or one marked as compatible with your specific battery type.
- Most modern devices charge faster on a wall outlet than on a computer USB port, because wall outlets deliver more power.
- Leaving a fully charged battery plugged in for days or weeks can shorten its lifespan, though most devices now have safeguards against this.
- Extreme heat or cold slows charging and can damage batteries, so charge in a room-temperature environment when possible.
- A battery that will not hold a charge after months of normal use has likely reached the end of its lifespan and may need replacement.
Charging a smartphone or tablet
Plug the charging cable into the device's charging port — usually USB-C, Lightning (on iPhones), or Micro-USB on older phones. Plug the other end into a power adapter, then plug the adapter into a wall outlet. The device will show a charging indicator, usually a lightning bolt icon or a percentage number on the screen. Leave it plugged in until the battery reaches 100 percent.
Charging from a wall outlet is faster than charging from a computer USB port because wall outlets deliver more power. If you are in a hurry, use the wall outlet. If you must use a computer, the phone will still charge, but it will take longer — sometimes twice as long.
You can use your phone while it charges, though it will charge more slowly if you are actively using it. If the device gets hot to the touch during charging, unplug it and let it cool down before charging again. Heat damages batteries over time.
Charging a laptop
Connect the laptop charger cable to the charging port on your laptop, then plug the power adapter into a wall outlet. Most laptops show a charging light on the charger itself or a battery icon on the screen. Leave it plugged in until the battery reaches 100 percent.
Laptop chargers are heavier and deliver more power than phone chargers, so they charge faster. A typical laptop battery takes one to three hours to charge fully, depending on the battery size and how much power the charger delivers. You can use your laptop while it charges.
If your laptop charger cable is damaged — frayed, bent, or cracked — stop using it immediately. A damaged charger can overheat and create a fire risk. Replace it with a charger made for your specific laptop model.
Charging a car battery
A car battery charges automatically while the engine runs, so you normally do not need to do anything. If the battery is completely dead and the car will not start, you will need a battery charger or jumper cables and another vehicle.
To use a battery charger: turn off the car, open the hood, and locate the battery. Connect the red clamp from the charger to the positive terminal (marked with a plus sign), and the black clamp to the negative terminal (marked with a minus sign). Plug the charger into a wall outlet and set it to the correct voltage — usually 12 volts for a car battery. Leave it charging for several hours or overnight, depending on how dead the battery is and how strong the charger is.
To use jumper cables: park another vehicle next to yours, open both hoods, and connect the red cable to the positive terminal of the dead battery, then to the positive terminal of the working battery. Connect the black cable to the negative terminal of the working battery, then to an unpainted metal surface on your car's engine (not the negative terminal itself). Start the working vehicle, wait a few minutes, then start your car. Leave both running for a few minutes, then disconnect the cables in reverse order.
Charging wireless and rechargeable batteries
Wireless earbuds, smartwatches, and some other devices charge on a wireless charging pad. Place the device on the pad with the charging coils aligned — usually the center or back of the device. A light on the pad or device will show that charging has started. Leave it on the pad until the battery is full.
Rechargeable AA and AAA batteries charge in a battery charger, not in a regular device. Insert the batteries into the charger slots, plug the charger into a wall outlet, and leave them until the charger shows they are full. This usually takes two to eight hours depending on the charger and battery size. Never try to charge regular alkaline batteries — they are not designed to be recharged and can leak or overheat.
What to do if a battery will not charge
If a device will not charge, start by checking the cable and port. Look for debris, lint, or corrosion inside the charging port. If you see buildup, turn off the device and gently clean the port with a dry cotton swab or a small brush. Do not use liquid or force.
Try a different charger if you have one available. If the device charges with a different charger, the original charger is faulty and needs replacement. If the device still will not charge with any charger, the battery itself may be dead or the charging circuit inside the device may be damaged. At this point, the device likely needs professional repair or the battery needs replacement.
If a battery charges very slowly — taking twice as long as it used to — the battery is aging and losing capacity. This is normal after one to three years of regular use. The battery will eventually need replacement, but it will still work in the meantime, just with shorter time between charges.
Protecting your battery during charging
Keep the device and charger in a room-temperature environment while charging. Extreme heat slows charging and damages battery chemistry. Do not charge in direct sunlight, in a hot car, or near a heat source. Extreme cold also slows charging, so if a device is very cold, let it warm up to room temperature before plugging it in.
Avoid leaving a fully charged battery plugged in for days or weeks at a time. Most modern devices have safeguards that stop charging once the battery reaches 100 percent, but older devices do not. Constant trickle charging can shorten battery lifespan. Unplug the device once it is fully charged.
Do not charge a swollen or visibly damaged battery. If a battery is puffed up, cracked, or leaking, stop using it immediately and dispose of it at an electronics recycling center. A damaged battery can overheat or catch fire.
Frequently Asked Questions
Is it bad to charge my phone overnight?
Modern phones have built-in safeguards that stop charging once the battery reaches 100 percent, so overnight charging will not damage the battery. However, leaving the phone plugged in for weeks at a time can slowly reduce battery lifespan. Unplugging once it is fully charged is the safest habit.
Why does my battery charge faster when it is warm?
Chemical reactions inside a battery happen faster at higher temperatures, so the battery accepts charge more quickly when warm. However, heat also damages the battery over time, so charging in a cool room is better for long-term battery health even if it takes slightly longer.
Can I use a fast charger on any device?
No. Fast chargers deliver more power than standard chargers, and using one on a device not designed for it can overheat the battery and damage it. Always use a charger marked as compatible with your specific device model.
What does it mean if my charger gets hot?
Chargers naturally get warm during use, but if it is too hot to touch comfortably, unplug it and let it cool down. Excessive heat means the charger is working too hard and may be faulty. If it continues to overheat, replace it with a new charger.
How long should a battery last before it needs replacement?
Most phone and laptop batteries last one to three years of regular daily charging before noticeably losing capacity. Car batteries typically last three to five years. Once a battery will not hold a charge for a reasonable amount of time, replacement is usually the only option.