Picture of Lithium Battery Solar USB/ iPhone/ Arduino Charger

One of the most fun and useful projects on instructables is to create your very own solar USB/ iPhone charger. They're not overly difficult to make, nor are the parts overly expensive or hard to find. For the most part they do a rather good job of charging up small gadgets. Mostly.

The big flaw in the DIY solar charger world are the batteries. Nearly all the designs on instructables (including all of my designs) use standard NiMh rechargeable batteries. They're cheap, easy to find, and very safe to use. The problem is that their capacity and voltage are both low, and the gadgets we keep wanting to charge are getting bigger and better batteries.

For instance an iPhone 4 has a 2,000mAh battery inside of it. Now that isn't too tough to charge up decently with a well made solar charger using 2 or 4 AA batteries. On the other hand an iPad 2 has a 6,000mAh battery pack on it. Not so easy to charge up.

The solution for these problems is to ditch NiMh batteries and turn to Lithium batteries.

In this guide I will show you how to make your very own Lithium battery charger. One that is cheap to make, easy to build, and most importantly safe to use.

(Oh and help me win the Instructables Green Tech Contest by voting for this project! An iPad would be great for my classroom! Even better, I'll build a massive Lithium powered charger to run the iPad. It'll be 100% green in my classroom.)

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* Zener 1n4734 5.6v
I was wanting to ask about the blocking diode no-one really explains why you pick that diode say over zener diode 1n437 5.6v. The reason i ask is iam attempting to build my own solar charger still waiting on alot of the parts to arrive. the solar cell will be 5.5v 266ma going to 4x 18650 cells in parallel setup. Will the zener diode that i have choosen work for the solar cell that i have.
Avani Balaji3 months ago
colbtron11 months ago

Adafruit has some sweet Li-Poly batteries which work well. What I'd like is to be able to add a LED strip to show how charged the battery is.

This worked very well for me. I simply just wired my battery up to it in parallel with the booster circuit.


JoshuaZimmerman (author)  colbtron6 months ago

Unfortunately, you can't just add LEDs in and expect it to show a charge. You'd need the right kind of voltage meter or monitoring chip. You could easily wire in a small LED voltmeter (they're all of $4 on eBay) and that would give you a general idea of how charged it is. Otherwise the charge controller board shows when it's full.

can you wire the lithium bateries in series???

raceteam364 months ago

where would you put an analog volt meter in this project

raoul.ursum5 months ago

How did you prevent the lipo from discharging under 3 volt?

tomasvega5 months ago

Hi there! If I use NiMH batteries instead of Lithium batteries can I just do not use the Charge Controller, connecting the Solar Panel directly to the batterie?

Mr_Rep1 year ago

sssoooo.... wheres the lithium kit from the video on the website? all i see is this massive and expensive unit that has dual charging ports. where can i buy a kit that uses a simple Li-ion battery, and one usb connection fairly cheaply?

JoshuaZimmerman (author)  Mr_Rep6 months ago

The parts are all still on the website. The new version addresses several issues that customers had, and gives a higher output and better charging. (The old version couldn't charge a tablet due to low amperage output. The new version can.) The prices are about the same as well between the old and new version.

avelyn9410 months ago

what if i wanted to put 2 output port how should i connect it?

JoshuaZimmerman (author)  avelyn946 months ago

I actually have a 2 USB Port, higher output, circuit board on my website. IT works better with lithium batteries then the version I used in this write up years ago.

kamhagh10 months ago

how can i charge & use the lipo to charge my phone at same time? (solar charging Lipo -> lipo charging phone -> )? at same time while walking :) (panel installed on my bag or something, or cars front window)

JoshuaZimmerman (author)  kamhagh6 months ago

That you can.

addisonday7 months ago

How would I add a switch on to this?

JoshuaZimmerman (author)  addisonday6 months ago

It depends, what would you like the switch to do?

edrisamiry7 months ago
hi plz answer me plz can I connect 3 or 4 AA batteries directly to the usb if not!can u please tell me what else can I use!I can't find charging controlers I cant access these things I m living in Afghanistan! can u plz plz help me make this stuff with easiest things!do you know I m talking resistors and other things from recycle electronics plz help me if one of u guys know! my email idris.amiry@hotmail.com BEST REGARDS: Edris
kamhagh10 months ago

how can i charge & use the lipo to charge my phone at same time? (solar charging Lipo -> lipo charging phone -> )? at same time while walking :) (panel installed on my bag or something, or cars front window)

gluvit11 months ago
Great project
Mr_Rep1 year ago

rather than the DC-DC USB Boosting Circuit could i just use the guts from a cigarette lighter usb charger? since it contains the 5V regulator

Mr_Rep1 year ago

rather than using the DC-DC USB Boosting Circuit, could i just use the 5V regulator from a cheap cigarette lighter usb charger?

jjjacala1 year ago

where i can get a free battery charger contorler?

jdw1001 made it!1 year ago

I made this neat little charger but I need a little help. It works fine with my old Ipod but it won't charge my Iphone 5. I bought the booster from BrownDogGadgets and modified it by taking out the battery contacts. ( I may have bought the wrong booster) I am working on making another one. But anyhow I found that this circuit would charge my Iphone 5 as long as I had the circuit in line with my car battery as it charged the Lithium Battery and my phone. That tells me that everything is all right. I just need more power or current flowing. I am considering adding another battery to the circuit. Any advise is greatly appreciated.



Just wondering because I can't seem to find this directly answered anywhere. Is it ok to be charging up your batteries via usb or solar while using them to power whatever you have plugged into them?
Nothing bad will happen if you do both at the same time. It's not going to harm the battery.

Your'e just sucking power away before it even hits the battery.

Will this then confuse the charge controller?

Is it thus necessary to use another type if charger? Like this one: http://www.adafruit.com/products/259

callega1 year ago

Thanks for this great project! I'm going to try it!

I have two questions:

1. There is a problem if you have connect the USB input and the solar panel at the same time?

2. It's possible to have connected any input source and charging a device at the same time?

Thanks again

1. I believe it is no problem as long as you protect your solar panel with a diode. However, the solar panel would only be able to contribute any power if the voltage is higher than the input USB power of 5V. Onto this the threshold voltage of the diode needs to be added too.

2. That is a good question. I found a forum post where the different possible szenarios for this setting are described: http://www.societyofrobots.com/robotforum/index.ph...

Moreover, there are special charge controllers which can connect batteries AND load together with a power source for charging: http://www.adafruit.com/products/259

Unfortunately, I haven't found any cheaper alternatives. Therefore I have a question too:

Is it possible to build such a thing as DIY so that it also works for higher charge currents?

I found a cheaper way to get the items needed. I got a 12,000mAH battery and a lithium charge controller/3 to 5 volt Booster circuit and a case for $18 on Rakuten and I also got a 6 volt 320mA Solar panel on Ebay for $8.

Hi there, not sure if you're responding to comments, but I am trying to reuse an old iphone 4 battery for this project, and the contacts are very confusing! I was wondering if you had any experience with this? Mr Google couldn't help me out this time...

JoshuaZimmerman (author)  lifeinbeats1 year ago

Not a good idea. I sent you an email about it.

pcrotts made it!1 year ago

Super fun to make. I got too big of a switch, but all is well. I taped two old phone batteries (1000 mA each) together for power.

Cats Science Club made it!1 year ago

Joshua does an amazing job explaining everything he does. Thanks to him we found a love for instructables. Take a look at what we made with a great instructable showing us how.



Cats Science Club,

Can I ask how you added the On/Off switch to your. What did you wire it to/from? Thank you.

Thanks for noticing the slight change! We have the positive from the lithium charge controller going to the switch and then to the positive on the usb port. In our picture the usb is covered with hot glue. We added the switch because the small red usb light being on all the time was draining the battery slowly. I believe Josh Zimmerman sells one with out a light or shows how to take it off the one he sells. Let us know if that helped and check out our site at catsscience.com!

taylorjr1 year ago

Thank you for the detailed project. I've zero interest or knowledge of electronics prior to finding this site, now i'm stoked about building this and I have all the pieces to make my first project...at least I think so, we'll see. Thanks again for peaking my interest in something I think I can really use and will benefit me to have.

But please help, Can I use double AA batteries with the lithium charging board, if I use 3 aa batteries i'll be at 4.5V, shouldn't that work? I already own many rechargeable AA's and zero lithium batteries.

My reason in wanting to try this is for the lighting indications. I'll know when fully charged and they wont be over charged, etc.


I followed your project but I am having a problem with the phone battery not charging even with phone off. I wired this as to the specs and double checked....Do I need to put another blocking diode to the USB controller?

By the way, I like this solar charger.
We have used usb circuits that worked find for everything but Apple products. Could it be your usb circuit? Like it was for us. Is the battery on the charger fully charged to start with? Good luck!
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