Emergency Charge a Phone With a Spare USB Cable.

About: A Northern Ireland based maker with a propensity to cause trouble and freshly constructed family.

The other day my phone, which is on its last legs ran out of battery while I was expecting a few important calls and texts that would need replies fast, I was in tech with no phone charger and wouldn't be home for another six hours so I did this... 

*WARNINGS* The course of action in this instructable is potentially dangerous, may damage your phone or its battery, will certainly void the warranty and has the potential to cause fire, damage and personal injury, I cannot and will not be held responsible for any injuries or damages incurred, consider this course of action a last resort and use your own common sense and initiative to try and solve the problem without resorting to such methods of phone charging. 

On a side note these methods can work for any device like an MP3 player or the like. 

Also if you can use the devices own ports, as any device that can be powered and charged via USB cable will have a built in system for controlling the battery charging, negating a lot of the risks of charging a lithium battery without proper safety measures...

Plus you should be able to do this with any phone charger or the like, however USB cables are cheaper and easier to find...

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Step 1: Find a USB Cable.

Find a USB cable.

Now cut the cable and separate the black and red wires inside, strip the ends of the black and red cables. 

Step 2: Determine the Pinouts on Your Device.

Googling "circuit diagram for ********** connector" should provide you with results, sites such as pinouts.ru and its english counterpart are excellent places to look.

I'm using a sony ericsson in this 'ible - There are two +5v ins, one is charge and one is USB, we need the charge one in this case, along with negative, the image below has them detailed.

This method is relatively safe, since the device will usually have circuitry in place to safely charge the battery.  

Step 3: OK, You Can't?

For some reason you can't charge your device,  maybe it has an awkward port like an old nokia or some such. 

Take out the battery.

Step 4: Use the Battery Terminals Directly.

This one is potentially dangerous, you'll want to keep the battery in your hand and stop any time it becomes hotter than normal charging makes it.

Basically you touch the terminals against the corresponding wires - with lithiums especially make absolutely sure you have the polarities correct and do not touch the middle terminal with the wires, as this can potentially damage the battery's functionality with the device and stop it working even if it's not broken.  

Step 5: Be Smarter.

Don't leave the charger at home when you can bring it, remember to charge your devices for when you need them...

When it's needed this stopgap measure is very useful for saving a situation but overall can't be considered an effective charging method.  Also never leave the device or battery unattended while doing this, since it's possible to cause a fire quite easily. 

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    23 Discussions


    1 year ago

    if you're charging by directly connecting to the terminals of the battery, nothing bad should happen on newer phone batteries since they usually have some circuitry that breaks the circuit when the battery is full (just as they cut out when the battery is empty). And concerning amperage - if you're charging a normal battery from a normal phone, say a battery from Samsung Galaxy S II, it should be capable of swallowing 500-1000mA that a typical charger provides.

    1 reply

    Reply 1 year ago

    still monitor it's temperature and voltage, I guess, just to be sure :D

    If you connect a 5V supply to your Lithium Polymer battery directly, this likely happen : http://www.youtube.com/watch?v=SQ0SNESIkWk 

    Be careful.

    1 reply

    Reply 1 year ago

    Yes. However, you're not really connecting 5V directly when you connect to a typical power pack from a phone or whatever else. There's a whole bunch of circuitry that takes care of breaking the circuit when the battery is empty/full and taking care of the charging process.


    9 years ago on Step 4

    o.O yeah, be VERY careful doing this. Usually the phone will charge it at less than the battery's output charge, less than 3.6v in this case, and with much less amperage... Look up 'overcharge li-polymer battery' on youtube sometimes, these things can turn into a blowtorch pretty fast. My guess is the battery might be damaged, even if it did charge. Still good for emergencies though, if you have to :) Interesting instructable.

    2 replies

    Reply 8 years ago on Introduction

    I'm pretty sure the phone has the battery charging circuitry inside. its why you can charge it via usb if you need to, think how the ipod or iphone works. :)


    Reply 9 years ago on Step 4

    I covered the safety issue on lipos at the intro, though they are capable of exploding they're not that dangerous as long s you use some common sense when charging this way and don't get them too hot it'll be fine

     First off, using the contacts on the phone is perfectly safe, as long as you use the right ones, any phone with USB connectivity charges at +5v from the charger too. 

    Admittedly there is a danger with the direct charging of a lithium battery with the wrong voltage, however it's stressed plenty in the instructable and doesn't need repeated so many damned times.

     Yeah, the battery directly seems like a bad idea, could it ''pull'' too many amps from the usb port and ruin the usb hub?


    Reply 9 years ago on Introduction

    well technically speaking, USB specs say that USB ports are designed to withstand a short circuit for an indefinite period of time. Also, USB ports are only supposed to supply a maximum of 500ma and only after the device has requested the extra power. But most ports and devices don't bother asking before they attempt to draw 500ma. I say most because RIM Blackberries are the only phone, that i know of, that will wait for confirmation from the USB host before drawing the 500ma and charging the battery.

     Well that was a completely depleted battery and it didn't pull enough to set off the power surge warning, all USB hubs are limited safely by the computer's OS so it can't exceed 500ma. The computer automatically disables power to the port until you remove the device and then choose to reactivate the port.


    9 years ago on Introduction

    I've directly pulsed charged LiPo, Nicads and NMH batteries from the car battery before, you just have to understand the danger and be careful.  Just used a couple of wires from the cig lighter and pulsed it to the terminals of the battery.  A few mins of this usually gives you plenty of time to talk in an emergency.

    1 reply

    9 years ago on Introduction

    Alternative option. Some hotels have like a box full of chargers that have been left behind accidentally by guests. If you pass by one, they may be accommodating if they have one that fits.