How to charge your phone with a 9-volt battery




Well, some car chargers will deal with a voltage this low but I wouldn’t count on all of them. Similarly a 9v battery won’t source the amperage desired by your cell phone for very long and depending on your cell phone/usb power supply combination, it won’t source enough at all.


These chargers are overwhelmingly built around the venerable and extra-cheap MC34063 chip.

Reverse-engineering and a mod of one here:

I modded one such adapter to use a 5.5/2.1mm standard barrel jack connector (used almost everywhere, good as an ad-hoc standard - another handy mod is doing the same with laptops, as then you can mix and match the power supplies), changed it from one to two USBs, and added one microUSB pigtail. (Another trick is modding the 5V-powered equipment to microUSB connectors. Instant compatibility with all smartphone chargers.)

I use a 12V/2Ah 3S1P battery as a portable power supply. A laptop battery can be modded for the same purpose. Or, if you have a balancing charger, you can make your own battery from 18650 cells salvaged from dead laptop batteries (sometimes, quite often, all that’s dead is a single cell pair and you have two more pairs with quite a lot of life remaining, for free).

It should work for a while from a 9V battery.


Yeah, i was wondering about the effectiveness of the charging method. They show that current does go through the set up and that the phone responds to said charge. But what’s the efficiency of the method? What needs to be done is to take a fully drained phone and attach the 9v battery. How much does it charge, if at all? How long would it take and how many batteries would you need in order to be able to: 1) turn on the phone and place/hold a call 2) time to at least send a text.

If a video cant answer these basic questions then this hack is misleading and potentially dangeous to people in survival or emergency situations. Show a method that is proven to be helpful. Not saying it doesn’t work at all, just that there’s no concrete information tied to the video.


I would say it has a pretty good chance of working in most situations.

As of danger, it adds some only and only when you rely on that method in advance; then its failure decreases your chances. If you don’t rely on it, and are improvising, its success increases your chances.

For concrete information, we’d have to measure the discharge characteristics of several batteries from multiple manufacturers, preferably more of each type, and measure the current requirements for different types of phones, and get the average/impulse current requirements, preferably as scope traces. There are many many variables here if you aim for real reliability.

…what I would love to see is charging circuitry directly in the phone that could take anything from 1.5V battery to 24 volts from a truck, and could adjust to optimal power point (current/voltage) of the source (for optimal efficiency of an attached solar panel)… maybe in some survival-grade models?


Why? Because someone going into a dangerous situation is going to pack a 9V battery, car charger, and key for this purpose, instead of a dedicated charger?

The purpose of this hack is to try and charge your phone when you didn’t expect to need to, and only have these things at your disposal. In that case, if it doesn’t work then you’re no worse off than if you hadn’t seen this video at all. So how can it be “dangerous?”

Regardless, most modern phones will not display a charging symbol if they aren’t al least being charged a little bit. If your phone shows a charging symbol, juice is getting in there, even if it takes you 20 minutes to charge enough for a 3-minute call.


Just keep a 7805 regulator in your wallet:
78xx - Wikipedia, the free encyclopedia
uA7800 Series (Rev. J) - LM7805.pdf


I love these things, wasteful as hell being linear but they are cheap, tiny, I think go up to 36V, best of all no RF noise, just need to deal with heat as that is where the extra volts go is right out the heatsink.


Not so crazy these Russians, I think!


Not as good idea. It can save your posterior but you have two major problems (neglecting the wire attachment as that can be easily-ish improvised). A buck converter is preferred strongly.

First, the efficiency sucks. With 9 to 5 volts, you lose 4/9, almost half, as heat.

Second, which is related, the thing will heat up like crazy at higher power losses. At one amp of charging current, you get four watts to dissipate. A bare TO220 has 19’C/watt. At four watts it is almost 80’C above ambient; at 20’C ambient the package can boil water and make not-so-nice 1st to 2nd degree burns. So heatsink is advised more than strongly.

You also may need the input and output capacitors, as the thing may be prone to oscillate at certain conditions. (Beware of those high-value low-ESR ceramic ones, they may not help that much as the chips aren’t designed for the low ESR and may oscillate anyway. I did not understand the plots/charts in that article that spoke about it, though, so had to just believe.)

You can get a DC-DC converter into smaller space, and with the MC34063 perhaps even into comparable cost, as a 7805 with adequate heatsink.

That said, these are fairly adequate for lower voltage loss and lower currents. I have such adapter for my (now misplaced, todo: find that bugger) 1000fps camera, housed in a piece of rectangular aluminium tubing with glued sheetmetal faces; surprisingly useful trick for its simplicity and the boxes are very structurally sound and can double as heatsinks, as long as they won’t heat above the temperature when the glue gives way (You can use epoxy but then the inevitable reworks/repairs get way more difficult. You can also fill the thing with a potting compound if the environment demands it.) Todo, write a special post about making these boxes.


Perhaps my wallet is made out of Solid Brass… and the prongs have some soldered wire stubs that I can just twist extensions onto… :wink:


The wire stubs would have to be on some sort of insulated material (to keep with the style I’d go for alumina ceramic tubes set into the brass block), but lower-end materials would do too).

The brass in this application feels a bit too heavy to me (but that can be part of the appeal for some users). However, it is also natively antibacterial (as also copper and silver are), which is a plus here.


Well, I could see it maybe being useful while backpack camping – my lantern uses 9-volt batteries. On the other hand, yes, often times you aren’t going to get a signal out in the wilderness – although you can sometimes be surprised where you can get signal.


The 9v battery is cool as it can be clipped in series to make an A battery for a portable tube radio set, I am surprised that things are still designed to use them.
that is why we have the weird battery naming conventions like no A or B but AA, AAA, AAAA, C, and D. B was the 120v(or whatever) plate voltage battery and the A was a big 1.5v dry cell for the filament.


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