Introduction: Lost Your Charger? How to Charge Any Battery Survival-Style

Picture of Lost Your Charger? How to Charge Any Battery Survival-Style

My camera shut down from low battery just when I needed to take some pictures.
The light was perfect. I suddenly remembered where I'd left the charger - 3000 miles away.
Everyone's had this experience, or the similar experience of spending one's vacation searching for a cellphone charger.

Here's how to charge any battery enough to keep doing the important stuff.

Fact 1: All past and future rechargeable batteries can be safely trickle charged if you don't overcharge them. Trickle means low current, like half an amp for an average camera or phone battery.
Fact 2: Small incandescent bulbs such as flashlight bulbs and christmast tree mini lights make great current regulators.

This is the battery to my Canon S30. It's got three terminals, labeled "+", "-", and "T".
I've clipped alligator-clips onto the two obvious ones.
You don't need clips, you can just hold wires on it for as long as it takes to charge, that's probably better anyway, so you can tell if anything is going wrong.

Warning! Wear eye protection and if anything weird happens don't breathe the fumes!

Step 1: Hands on Charging

Picture of Hands on Charging

What was that other terminal marked "T" for? TIMMY of course, just like in the nursery rhyme!
It's for Timmy to to hold his finger on the battery. If it gets hot you're doing something wrong.
Actually it's "Thermistor" or similar names. Temperature sensor. Some batteries use that to regulate charging current, some just for a safety feature.

"Digital sensor, huh?" would be a running joke back when Americans knew Greek and knew that digits are fingers. But then numbers got so much use we forgot about counting on fingers, and now people barely know how to do anything with their hands.

Anyway, here's a finger used as a digital thermometer. Which reminds me of the joke about the doctor...

Step 2: Charge From Car Battery With Lightbulb Regulators

Picture of Charge From Car Battery With Lightbulb Regulators

SAFETY WARNING: scroll to the bottom if you want to read safety warnings.

Here I am charging my camera's battery from my car battery. I'm using three christmas lightbulbs at once as a current regulator to get half an amp to flow into the camera battery.
Here's how it works:
As the current through a lightbulb increases, the filament gets hot. That increases the resistance, which limits the current.

For example, here's my test of one of these mini christmas lightbulbs hooked up to a bench DC supply:

Volts Amperes
.5 .05
1 .07
1.5 .08
2 .09
3 .11
4 .13
5 .15
6 .16
7 .17
8 .18
9 .18
10 dead. The filament burned out.

I tested two bulbs and the data was the same.

Since my car battery is at ~13 volts and the camera battery is at ~7 volts, there will be 6 volts across the bulb. So I put three bulbs in parallel to get about 0.5 amperes to flow into the battery.
I'm guaranteed that less than 0.6 amps will flow, because that would burn out the bulbs.
That's some protection against reverse-charging, but do make sure you connect the plus terminals and minus terminals correctly.

Now just stand there for fifteen minutes or so until your battery is charged enough to take pictures again, you can make calls on your phone or whatever.

Do not leave this unattended, and don't attempt to fully charge the battery.
If you charge too long and your camera battery gets over 8 volts, bad things could happen.
"Bad things" include possibly catching on fire.
Repeat: you can safely trickle charge any rechargeable battery part way.
But it is NOT SAFE to fully charge a battery without fully understanding the rules for that specific type of battery.
Car Batteries can produce a mixture of oxygen and hydrogen which can be ignited by a spark.
The resulting explosion sprays sulfuric acid everywhere. Don't let that happen to you. For simplicity's sake this photo shows me working right on the battery, but you could just as easily get your battery voltage from the cigarette lighter inside the car, far from the explosion hazard.
Also, don't electrocute yourself. I haven't heard of anyone being electrocuted by a car battery. I have heard of the other accidents described here actually happening.

Step 3: Charging From Any DC Source and Resistor

Picture of Charging From Any DC Source and Resistor

Hopefully you own an electrical meter.
Find a source of DC electricity. Look at the voltage of your source, the voltage of your battery, and use Ohm's law to figure out what kind of resistor you need to put between the two to get the right current to flow. Then go find that resistor. A piece of a heating element from a toaster or hair dryer can work. That clothes iron in the photo worked for a certain battery and a certain DC source.

As seen in the previous step, the best improvised current regulator is usually a small lightbulb. The bulb is great because the resistance goes way up when the filament gets hot and limits the current. And you can only put an amp or so through one without burning it out, so it acts as its own fuse. And they're free gifts from garbage Santa.

Here I'm using two bulbs in series to limit the current going into a gelcell. Use your multimeter to measure what current goes through your bulb at different voltages. Or you can just cowboy it and use one tiny bulb for a few minutes, while feeling to see if the battery gets hot or not.

Wear eye protection and don't breathe the fumes!

Step 4: Current and Voltage From a Bench Supply

Picture of Current and Voltage From a Bench Supply

This step uses a bench power supply to charge a battery. A lot of us have those sitting around even if we can't find our cell charger. Or we know where to find an electronics guy who has one. Now what?

Want to be totally mystified? Look up "lithium battery charge control".
All that stuff is important if you want to fully charge your battery, make it survive many charge cycles, or avoid lawsuits.

But we just want to take pictures or talk on the phone. So here's what we do:
Turn the current and voltage knobs all the way to the left. Turn on the powersupply and
hook it up to your battery, bearing in mind that red and black wires can possibly be plugged into the wrong sockets. Read the labels and unplug it if it seems to be arcwelding on your battery.

Turn up the voltage and current limit knobs until 500 milliamps (0.5 amps) is flowing into your battery. If you feel like being careful look up how much current the experts use.
But half an amp for a few minutes won't damage any battery that's big enough for a modern camera or phone.

My electronics guy told me to set my voltage limit to 8 volts for my 7.2v li-ion battery. Usually facts like that are luxuries. The point of this method is to trickle charge anything without being able to know much about the properties of the battery.

Step 5: Time Limit

Picture of Time Limit

If you really have to do something else while charging your battery, you better hook up something to disconnect it after a few minutes.

The whole point of this instructable is that we're not going to fully charge the battery because we don't know how, and we're in a hurry.
We're just going to charge it enough to go back to our regular jobs. The phone or camera will tell us roughly how charged the battery is after we start using it.

So we're only going to charge it for ten minutes or so.

My camera battery has 1200 milliamp/hours of capacity. So if it's fully discharged and we charge it at 500 milliamps, it would take more than two hours to fully charge it.

Some types of batteries can be badly damaged by overcharging. Some are just damaged a little.
This picture shows how my golf cart avoids overcharging. There's a built in appliance timer that turns off the charger automatically. It won't let you charge for more than 24 hours.

That's it! Enjoy cautiously!
To make your own external battery pack, check out AT's splefty booster pack.


PhilM8 made it! (author)2015-07-29

My vape battery (18650 Li-ion) was dead, I was out of cigarettes, and I could feel the nicotine cravings starting to creep up on me. So, I decided to rig this little bad boy up. Thats a regulated variable voltage power supply set to 4.12v to be safe so theres no chance of overcharging. Multi-meter on the left is measuring amperage draw, one on the right is monitoring battery voltage. Battery is charging nicely, not getting hot, etc. Samsung's specs for the 25R state that it likes to be charged between 1 and 1.5 amps normally, with a maximum constant charging current of 4 amps. So no problems there! When the multi-meter on the right shows 4.12v, then its time to take the battery off the charger. With how volatile I know Li-ion batteries are, my electronics background questions this idea, but my nicotine cravings say "GO FOR IT!" As long as its properly monitored, I don't think we'll have any issues.

Derpy_D (author)PhilM82017-05-08

vape batteries are known to explode when charged with the wrong charger

Americanguy2785 (author)PhilM82017-01-29

Smart! I vape to amd would of done the same sh@t to get nic

Alden Tortem (author)2017-02-17

Actually we can recondition battery - using this method. Thank you Gregory ! :)

M L G (author)2016-06-25

How many bulbs would I need for resistance if I was charging a 3.7v lithium ion cell? Also could I cut the end off a spare charger and attach the wires to the lithium ion terminals? I understand that it's not easy knowing which of the wires is which in these mobile phone chargers, but my problem you see is the charging port! Tried to desolder the old one and I think I've stuffed it up! So instead of throwing the tablet away I thought might try fix it or in this case break it further and then ask expert whether it's salvageable?

Graham30rad (author)2016-03-18

Can anyone tell me I can charge an 18v lithium battery with a 21v lithium charger?? Or would it cause me heartache? (It's for a cordless drill)

SharonC52 (author)2015-11-23

can you recharge a rechargeable battery in the refregrator?

SharonC52 (author)2015-11-23

can you charge a battery in the refregrator?

adamwoodband (author)2015-04-25

or just buy a couple extra batteries and maybe two battery chargers, solar charger, and a car charging station. If your a field freelance and assignment photographer I feel like maybe that is the solution. Learn once, feel bad for a little that you were not prepared and then correct and move on.

simon.gilmour.58 (author)2015-03-19

Doesn't work, of course.

DaniyalA1 (author)2015-01-08

I didn't have a phone so I connected the charger to the battery directly. Using a formula I found out the time to charge the battery completely. It took three hours. Mine was a BL-5C battery (1020 mAh). Thanks for the help!

AlexB8 (author)2014-11-19

You can use a unregulated power brick pretty successfully too. Find a DC wall adaptor with a close voltage and amperage setting to the battery. Because it's unregulated, the voltage will drop to match that of the battery, but the current will increase. You can check to see if it's unregulated by measuring the voltage from the adapter, if it's higher than what it's rated for with no load, it's probably unregulated. As long as you don't go too far from what the adapter is rated current wise, should you be safe. Li-ion batteries have a unique charging profile, where the voltage and current needed to charge depends on how far along the charge is. As your battery charges, the voltage will climb, and the current will drop. This is the basic charging profile for Li-ion. You don't want to overcharge Li-ion batteries. Once the voltage reaches around 4/4.1 for a single cell, I'd call it quits. Remember you're trickle charging. You're only trying to put on a small percentage of current compared to the battery capacity. When I've done this in the past, I use a multimeter to measure the voltage, and one to measure current. I wouldn't do this without one to at least measure voltage. If you don't have one to measure current, make sure the wall adapter isn't getting too hot. Don't stray too far from your operation either.(don't leave home) Disclaimer: Intended for informational purposes only

LadyAtTheL (author)2014-11-17

Thanks! I have a great cordless drill and the charger died. They don't make the battery anymore so there aren't any replacement chargers that fit it. I will explore options using my trickle charger.

himanshi sharma (author)2014-11-15

What to do if we had no charger for battery of samsung galaxy fir

technogumbo (author)2008-07-12

I think Tim does a decent job of explaining the risks involved. I think I would give it a shot if I were in a jam. I would only use a very low amp source to do this though. Doing it with a car battery is too shaky for me.

matroska (author)technogumbo2014-07-13

Indeed the risks involved are well explained. It is true that a car battery is capable of supplying many, many amps, should something be wrong so using a low amp source would indeed make this much safer.

In fact, if you're stuck with a battery that is a single-cell lithium, voltage from a USB port should be sufficient (5V, single cell is 3.7V) without further current regulation (a 'normal' computer port is already regulated at 500mA at most; modern dedicated charging port can go over this specification and often reach 1A). If however your battery is multicell (often, 2 cells in series, 7.4V) then I guess you could fall back to a 12V battery or low current adapter.

davegriff (author)2007-10-20

Thats a pretty dangerous way to charge a lithium battery. Ever seen one burst (explode!!) into flames. Any way, if it doesn't self destruct it certainly won't have a very long life using this method of charging. DONT ATTEMPT THIS

matroska (author)davegriff2014-07-13

I believe the danger of explosion from lithium batteries comes from their very low internal resistance, which may permit a ridiculous current to flow if the proper conditions are met (e.g not regulating the current and applying a higher voltage to the cell, or short-circuiting the cell).

In this case, lightbulbs are used as a crude way to limit current. OP stated he used at most 0.6A for a limited time, while checking on the temperature, which is all reasonable. Modern smartphones batteries will today charge commonly at 1A and sometimes 2A (larger phones or tablets).

Of course this method will not permit you to fully charge a lithium battery because, as stated, lithium batteries need a specific charging profile to be fully charged (which is clearly not applied here). However this method works for charging a cell to a reasonable level which will allow a good level of use, perhaps even 80% if one checks the time and monitors the temperature.

KahlZun (author)davegriff2010-02-26

Unless you really have to.

Toga_Dan (author)2012-12-26

Some electronics do not have removable batts. I wonder if there is a way to safeguard the electronics if you need to do this with an e-phone, kindle, etc.

Ideas on this?

iamdarkyoshi (author)Toga_Dan2013-04-29

if its a kindle fire, it can be popped apart quite easily. as for an iphone, dont buy crapple, get an android :D

Toga_Dan (author)2012-12-29


Toga_Dan (author)2012-12-26

Nice idea. Did you check the current flow on your setup with a meter to confirm your math?

MasterErik (author)2012-11-27

IKR. Shorted my distributor in my old Honda once hooking up an old style flash timer. My right arm was thrown up and hit the hood REALLY hard. Knocked the hood off the support rod and then that hit my other hand. As my right hand continued to circle back around behind me then it pulled me back from the car. Glad it was the cheap 8000volt option...

fma_battery (author)2012-04-12

It is better to learn the fully charged voltage of the battery:
1. 1.2V Ni-MH/Ni-Cd, fully charged voltage should be 1.54-1.60V per cell;
2. 3.2V LiFePO4 (LiFe) battery, should be 3.65V per cell;
3. 3.7V Li-ion or Li-Polymer battery, should be 4.2V per cell;
And certain charging time is necessary, it is about:
(1.2~1.5X Battery Capacity)/Charging current.
Otherwise, battery maybe leakage, hot heat, damaged or explode!

harlyquin (author)2010-12-07

no one's killed themselves from a car battery because it's DC and won't stop your heart. The only part of a car that can kill you with electricity is the alternator (the current has to pass through a bridge rectifier to switch to DC, so it can be used by the accessories and engine)
Don't get me wrong, you really REALLY don't want to ground out a coil pack or a distributor. It'll feel like having your arm yanked on while being covered in a shower of angle grinder sparks.

amchugh (author)harlyquin2011-11-09

harlyquin, you might want to youtube search for bush welding with car batteries... 90+ A/hours to some truck batteries with is well and truly enough to stop a heart (considering it takes 0.1Amp across the heart to do so)

lukeyj15 (author)harlyquin2011-10-14

I have been unlucky enough to take a brief spark straight out of a coil. Uncomfortable but not deadly.

ericcox (author)harlyquin2010-12-11

@harlyquin: DC current can most certainly stop your heart, just like AC. But not usually at the 12 volts that cars use. The resistance of your skin is fairly high (around 500K ohms if memory serves), so 12 volts isn't enough to cause much current to flow. But if your skin is wet or has other substances on it, the resistance can drop severely, to 1000 Ohms or less. And that can cause much more current to flow.

But it is NOT the fact that it's DC that makes it less dangerous - plenty of people have been electrocuted by high voltage DC. It's the fact that the battery voltage is so low. Coil packs can generate 50,000 volts or more - that's why they are more dangerous than the battery.

Just want to make sure that no one thinks that DC current is "safe", that's the way people get careless, and killed.

balisticsquirel (author)ericcox2011-01-12

Tru dat

Unfortunately it's not that simple either.
The characteristic of a power supply that makes it dangerous is actually the.. um ... power rating. And that's best determined from the current (Amps) rating. High voltage IS what will let the power supply (battery / whatever) overcome the high resistance (low conductivity) to get to your vital organs, but current gives it the power to do something when it gets there.
So any high current situation is dangerous, PARTICULARLY at high voltage.
And your car battery has plenty power to do serious damage under the right circumstances.

ericcox (author)balisticsquirel2011-01-14

I disagree. The power rating on a car battery would be around 7200 watts for one with 600 cranking amps. Much bigger than, say, the PS on an old CRT or a PC or a refrigerator. Yet compared to any of those things, the car battery is much less of an electrocution risk, because the voltage is only 12 volts.

The amount of current that can kill you is so small (anything over about 100 milliamps - that's tiny!) , that almost any power supply can kill you if it has enough voltage to push the current through your skin.

A 1000V power supply that can only deliver .2 amps is just as deadly - at least from electrocution - as a 1000V power supply that can deliver 100 Amps. The converse: A 12V battery that deliver 600 amps is not any safer than the same battery that can only deliver 5 amps.

balisticsquirel (author)ericcox2011-01-21

Which part do you disagree with? The bit where i agree with you, or the bit where i back up your comment that DC isn't necessarily safe (see that i said "under the right circumstances")?

The rest is semantic argument and probably not best suited for this thread. But i'd be glad to learn more if you want to message me.

ReCreate (author)2009-01-18

i have two lithium ion(i think) 3.5-3.7v cellphone battery cells and i want to slowly -safely charge it(like in 24 hours or so)becouse i dont want it to catch on fire

ReCreate (author)ReCreate2009-01-18

so how do i do it? Are there any ibles that show me how?

lukeyj15 (author)ReCreate2011-10-14

You'll need to find the charging voltage for the battery (try the manufacturer's website) and then apply a tiny amount of current. To work out just how much, divide the capacity of the battery (in mAh or Ah) by the time you want to spend charging. You then have the charge current in mAh or Ah and the amount of time required. Usually it's safest to take over 10 hours, but some Li-ion batteries can handle more. Better to be safe seeing as they can have quite nasty reactions to being charged too fast.

scienceguy (author)2010-07-15

I need to charge a 7.2 volt 1000mAh cell phone battery. I am at home and have a little over 100 different chargers but none match those numbers. If i take a charger that is below both those numbers, would the battery charge and still be safe to leave alone or be safe at all? Would it be best to get the closest match on voltage or mAh? And finally, what should i do to reduce the voltage or the mAh if need be? thanx

lukeyj15 (author)scienceguy2011-10-14

As long as the voltage matches, the current doesn't really matter AS LONG AS IT'S SMALLER THAN THE ORIGINAL VALUE. Because then it just takes longer. But a higher current means the battery could explode.

dpark76 (author)2010-04-25

I think these instructions were pretty well thought out, and would be rather useful for mechanically or electrically inclined people, and NOT for the average Joe.  These instructions help the "initiated" to think outside the box. Just like everything else in's a calculated risk.

Heaven forbid if I'm driving through the mountains and get stranded without my phone charger, and my phone dies, at least now I know i can hack together a few wires, and light bulbs to charge my phone to send out that brief but urgent SOS. That's empowering to know.

jay886 (author)dpark762011-03-01

Start keeping christmas lights in your car haha :]

lukeyj15 (author)jay8862011-10-14

Or your headlights. I hope you keep them in your car.

averagejoe1999 (author)dpark762011-05-15

I guess I cant do this...

KatherineFColes (author)2011-06-23

Now, I know what to do when I lost my charger again. This thing is very Big help to me. The charge current depends upon the technology and capacity of the battery being charged. For example, the current that should be applied to recharge a 12 V car battery will be very different from the current for a mobile phone battery.

This is a very important point some Protection Circuit Modules (PCMs) have an Overvoltage Protection that is close to the typical pack voltage. So applying 12V to a cell phone battery will have no charging effect.

papalevies (author)2007-10-18

...and you get to lose a finger if it explodes! I don't get the joke either...

KahlZun (author)papalevies2010-02-26

Another word for 'fingers' is 'digits'..

therefore, digital sensor could be interpreted as 'finger sensor'

bears0 (author)KahlZun2011-09-03

and "digital" thermometer, reminds him of a joke about a doctor. lol

love7421 (author)2011-05-26

Allow me to qualify myself, Associate, Bachelor and Master Degrees in Radiologic Sciences and now earning a PhD. I understand electricity far better than an electrician. This does not mean I can perform a complete house wiring but I understand what one can and more importantly, cannot do.

With all of that behind us, I have a lovely drill and I accidently threw out the charger for the batteries. No problem, I whipped out the 'ole car charger with both 6volts and 12 volts settings and a trickle setting for each voltage at 2 amps or a charge of 6 amps for bigger batteries, like a car battery as the manufacturer intended. I placed the charger on 6volt, 2amp trickle, tested temp, set a timer, and all is at peace now. Very easy fix just be sure to use the right setting, do it in the right place (not in your house), and right time (when no one else is around to get their fingers in the way like my son wanted to do).

The real fun was that neither the battery nor the drill listed which terminal was positive or negative. That is easy enough to fix because the charger has a built in indicator of charge and if you get it is obvious.

Do not be so scared, it is for individuals that understand electricity and know when to stop, however it can save you from a major problem if a device is dead and you MUST have it.

shama naz (author)2011-04-20

you r mad???

jay886 (author)2011-03-01

Or possibly cutting a USB extension cable and using the black and red wires in the same fashion on the contacts of the battery, but keep your eye on it.

4mikey4 (author)2010-10-31

I have an lg rumor and the charging slot broke off. I'm sure it would still work if I had a battery that was charged. Is there anyway I could use a standard car charger for this. Or would it be too much voltage?

About This Instructable




Bio: Tim Anderson is the author of the "Heirloom Technology" column in Make Magazine. He is co-founder of, manufacturers of "3D Printer" output ... More »
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