How to Charge 18650 Battery Without Charger? I’m Not Joking!

A battery charger has become almost as important to most households as their telephones are. The majority of things we use around our homes and offices use a battery to provide a portion of their power. From remote controls, to laptops, can openers, toys, speakers, and more we rely on the power from batteries to make our lives easier and more enjoyable.

How to Charge 18650 Battery Without Charger

We have learned that buying a rechargeable battery and a 18650 battery charger will save us a lot of money, a lot of stress, and a lot of tears when our children’s devices run out of power. We rely on our battery chargers to keep everything running smoothly, but what happens when we go on a trip and forget to take our chargers along with us? Do we have to revert to buying more batteries or is there a method we can use to recharge our batteries without our battery chargers?

Trickle Charging

Applying a trickle charge will work to recharge the majority of battery types. When you apply a trickle charge you are providing a very low electrical current that the cells of the battery can absorb. 

Trickle charging will take a long time to replenish a depleted battery but it can be done safely and it usually will do no damage to the battery you are charging.

You need a regulator to apply a trickle charge and luckily the small incandescent bulbs you find in flashlights and in ornamental string lights like Christmas lights make the perfect regulators for the job.

You will need to connect a wire to the bulb you are using and then the other end of the wire will connect to a hot battery, like a car battery. The car battery will send power to the bulbs and the filament inside the bulbs, (the bulbs must be incandescent) will heat up and when the filament heats up it creates resistance. The resistance created lowers or limits the amount of current that comes through the bulb so you can safely use the current that comes out of the bulb to trickle charge your device battery. You are going to need to connect the equivalent of three Christmas light bulbs, the small ones, at one time to create a current that measures one half of an amp.

Alligator Clamps

You will need small alligator clamps on the ends of your cables that allow you to connect to the positive and negative terminals of the battery you are charging. Remember that if you reverse the polarity of the battery while you are charging it. (If you hook the negative battery terminal to a positive charge or the positive battery terminal to a negative charge) then you are going to damage the battery and possible do harm to yourself.

If you do not have alligator clamps you can just skin back the wires on the cables you are using and then hold the skinned portion of the wire directly against the battery terminal. The terminals on your battery will have a plus sign showing the positive connection and a minus sign to indicate the negative connection.

When you use this method to charge a battery you are going to need to stay with the battery, even if you have alligator clamps connecting it, and you must disconnect the battery after just a few minutes. This type of charging can be dangerous so we must include the following safety warnings.


  • The batteries on automobiles, lawnmower equipment, ATVs and such are capable of being ignited by a small spark because they often create a mixture of hydrogen and oxygen that is extremely flammable. A slight spark can cause an explosion that sprays sulfuric acid under the hood of your car and possible on you causing mechanical damages to your engine, bodily damages to your car, and physical injuries to you.
  • You should not attempt to do this unless you wear safety goggles to protect your eyes from debris and fumes
  • If you charge your battery you cannot give it a full charge in this manner without risking permanent damage to the battery
  • Never leave a battery that is charging in this manner unattended for any length of time. There is a risk of fire and battery damage associated with charging in this manner so you NEVER walk away from a battery you are charging in this manner

Instead of connecting the battery and bulbs to your car battery you can connect them to the cigarette lighter inside your car and this would prevent the sulfuric acid explosion or possible damages to your vehicle or vehicle battery.

It is highly possible and probable that if you try to charge any rechargeable battery without the proper charger you will damage the battery and have to buy a replacement.

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