$9 Emergency Phone Charger 10 Minutes




About: I'm a computer engineer - but please don't judge me by that. I heat with wood, fix broken things and love camping with my family. I'm a closet solar nerd, love coupons, not scared to dumpster dive and love...

Power off? Grid down? Hurricane? Tornado? Camping? Apocalypse? Cross eyed lumber jack down the street?

I want to show you how to make a quick, simple and cheap DIY phone charger with basic tools and skills - anyone can do this. Shelf stable, clean - with no lead acid battery mess!

I used $9 in parts sourced at Harbor Freight and it took me less than 10 minutes.

Check out my guide to coupons and savings at Harbor Freight!

Please read about enhancing the quality of life for persons needing affordable prosthetics at the end of this instructible.


Step 1: Supplies Needed

Supplies I used:
12V dual outlet adapter - $4.99 on sale at Harbor Freight
(2) 6V lantern batteries - $2.49 on sale at Harbor Freight
Automotive fuse - on hand (recommended not necessary to work)
(2) Standard female terminal crimp ends - on hand (recommended not necessary to work)

Don't forget to take your 20% off and a free item coupons!

Cutting Pliers - but a cheap knife or scissors could be used in a pinch.

Not pictured:
Your phone's car adapter

*Note - I used the dual adapter because it was cheaper and I'll have an extra 12v outlet for a later project. This extension or this extension will do just fine too!

Step 2: Disassemble 12V Adapter

We need to separate the wires out of the adapter - but we need to know which is positive and which is negative. This is easily done with out any additional tool if we just take it apart.

Unscrew the cap on the 12V adapter.
Remove the fuse.
Pry open case and separate it from the wires.

Before cutting note which wire attaches to the center pin where the fuse was attached. This is our positive lead. Cut one positive wire off and mark it somehow. I tied a knot in mine.

Cut ground wire off at the soldered prong.

Step 3: Put the Batteries in Series

Put the two batteries in series. This is a fancy term for linking the batteries together in such a way that we double the voltage.

Put the two batteries together side by side. I put electrical tape on mine to keep them from moving - helpful but not necessary.

Measure a piece of the negative (ground) wire (the one not marked or without a knot) about an inch or two longer than the distance between one positive terminal and one negative terminal. Cut it with your pliers.

Strip away about a quarter inch of the insulation on each end of the wire. On battery 1 tip the spring on the positive terminal to one side and slide one end of the wire under the spring. On battery 2 tip the spring on the negative terminal to one side and slide the other end of the same wire under the spring. Place the terminal caps back on the used terminals.

Pro Tip: Series Vs Parallel
Batteries in Series: Connect (+) to (-) and double your voltage.
Batteries in Parallel: Connect (+) to (+) AND (-) to (-) and double your amperage - or the Amp Hours of your battery bank.

Both series and parallel should be done with matching batteries.

Step 4: Attach Adapter

Strip away about a quarter inch of the insulation on the adapter end of the negative wire. On battery 1 tip the spring on the negative terminal to one side and slide the other end of the same wire under the spring. This will be the negative terminal not used in the previous step.

Recommended but not functionally necessary

Add a fuse:
On the positive wire cut about 3 inches or so and strip a quarter inch or so off both ends. Crimp one terminal to one end. On the remaining positive wire still attached to the adapter strip off a quarter inch of the insulation and crimp on the remaining terminal. Put the one terminal on each lead of the fuse. *Note - please use a good fuse. See how the fuse in my photo is blown.* Put a small piece of tape around the crimped terminals to avoid shorts.

On battery 2 tip the spring on the positive terminal to one side and slide the stripped wire under the spring. This will be the positive terminal not used in the previous step.

Put in your adapter and charge up your phone.

Thesebatteries are inexpensive - but they house 4F batteries each. This will give you a total of about 28 amp hours at 12V. Roughly the same as 104 AA batteries.

This little DIY build hack is great for camping, an emergency grid down power outage or for my for my prepper friends to toss in the bug out bag/vehicle. Charge your phone inside in a pinch without spilling a lead acid battery all over the place.



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    23 Discussions


    1 year ago

    If you used the other extension with the clips and a 12v battery isn't that the same thing?

    Tater Zoid

    4 years ago

    This is perfect for an outdoor festival I attend. Now I can power my iPad for my photobooth without having to use a friends generator. Thank you.

    3 replies

    That would be a great use - actually a friend camping at a music festival asked me about charging her phone. That is what brought me to this. Let us know what batteries you use and how long they last for you!


    HF just moved into my neighborhood so I'm going to do my best to copy your instructions as close as I can.


    4 years ago

    is this a one time use only? or is there a way to recharge the batteries?

    2 replies

    They are not rechargeable, but this could be built with rechargeable batteries. It would cost more than $2.50 a battery though. Once they are consumed they would need to be recycled - however you should get a pile of recharges out of this bank. Thanks for checking out my build!


    Reply 4 years ago

    the circuit breaker on your house or your phone's replacement insurance are about the only things that should be used in place of a fuse.

    More CowbellTheBarton

    Reply 4 years ago on Introduction

    The adapter has an 8 amp fuse that is removed. If you used somewhere between 8-10 amps I think you'd never have an issue - unless something was wrong.


    Reply 4 years ago on Introduction

    you can easily omit the fuse, since your car charger is likely to be the first thing to let out the magic smoke.

    If you want to retain the protection of a fuse, you could use an automotive/marine breaker instead. If it trips, press the button to reset, just like your 110/220 house breakers.


    4 years ago on Introduction

    I notice you made no mention of the 120 ohm ?? resistor in series in the adapter . Can you really attach the 12volt of series batteries to the phone directly without damage or do the fuses take care of all of that. Chargers typically deliver about 5 volts.


    1 reply
    More Cowbellwkeller1

    Reply 4 years ago on Introduction

    Hey Wkeller1 - The resistor is not necessary here because you are actually using your car adapter between the battery series and the phone. Since the car adapter is set to run on a 12V input all is happy. (Most chargers will actually run on less than 12V, so you could probably get away with one 6V battery...) If we were dropping the voltage between bank and the phone we'd have to get creative. Thanks for checking out my build!


    4 years ago

    Luv it.


    4 years ago on Introduction

    How many charges can you get out of the two batteries? Are there rechargeable lantern batteries?

    1 reply
    More Cowbellblodefood

    Reply 4 years ago on Introduction

    Great question - sadly the answer is it depends on the phone, the amount of charge in the phone's battery and the activity of the phone while charging.

    Mathematically speaking lets assume you have a 1.9ah 1.2v iPhone battery or 2.28 watts / hour. The lantern battery bank is 12V and 28 ah or 366 watts / hour - so in theory if your iphone was off and you only charged it exactly the length of time it needed to be charged you would have 160 charges. This does not take into account discharge efficiencies, inefficient power draw of the adapter, plus their LED draw. These factors are completely unknown to me.

    But it is cheap, portable, shelf stable and quick to make in a pinch. Plus I think it is fair to say you will get several full charges. Do I think I'll get 5 months worth of charges? No - but I'd be very happy with a week...especially after going through the 2012 east coast derecho and 10 days of no power!