# Can a phone battery give power to another device?

Discussion in 'Power Electronics' started by Rumokiga, Nov 19, 2014.

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1. ### RumokigaGuest

Hi,

Hi I'm a real noob when it comes to electronics, I hope you can help me

So my question is, can a phone battery (more specifically a smartphone's) give power to a device that is asking for like 9 V, 4.2 Ah?

(sorry if I did post this thread in the wrong section, I went with the general forum to be safe )

2. ### Harald KappModeratorModerator

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Nov 17, 2011
Welcome to our forum.

9V? Yes, using a step-up converter.

4.2A? Unlikely. As you step up the voltage from e.g. 3.6V to 9V, you have to increase the current on the input side by the same factor. 9V/3.6V=2.5. Therefore the input currrent will be at least 2.5*4.2A=10.5A. I wouldn't expect any smartphone batttery to be able to deliver this much current. If it does, it will be drained in a few minutes.

By the way: Ah is not a currrent, but a capacity - the correct unit for current is A. If you really mean Ah, then the question makes no sense because from the battery's capacity one cannot simply derive the power requirements of the device.

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3. ### Christonio

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Nov 18, 2014
Umm maybe he could get the amps if he connected multiple batteries in parallel? What do ye think?

4. ### RumokigaGuest

Hi Harald,

I actually think it's Ah, well as I said I'm a real beginner so forgive my ignorance.

In more details, what I need to do is to make a defibrillator that can be powered by the smartphone's battery once plugged in, so I looked into some of the defibrillators that are in the market, like this one: http://www.medical.philips.com/main/products/resuscitation/products/onsite/specifications.wpd and saw that its battery power is of 9 V, 4.2 Ah.

So I was wondering what are the information that I should be looking for if it's not Ah?

Thank you

5. ### RumokigaGuest

Hi Christonio,

Isn't it possible using just one battery?

6. ### Christonio

8
1
Nov 18, 2014
WELP, it says it already has one battery preinstalled, so why do you need the another one? And if its Ah so 4.2Ah=4200mAh, and so one TABLET battery(those have great capacity) should work.

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7. ### Harald KappModeratorModerator

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Nov 17, 2011
That is not the power, that is the capacity, the amount of energy the battery can store. In the case of the defibrillator it is mostly a measure for how long you can have the device hanging on the wall before you need to re-charge the battery (although typically the battery would be continuously kept charged while the defibrillator is not in use).
You need to know the power consumption of the device in either watts (W) or Ampere (A).

As a defibrillator is a live-saving device, I can only recommend not to use any battery other than provided or listed by the manufacturer. You risk malfunction otherwise and you wouldn't want to be liable for a life lost due to a wrong battery.

8. ### RumokigaGuest

I need to BUILD a defibrillator from scratch (or almost) so I won't use the Philips device, I just checked it to have an idea on how it works.

9. ### Harald KappModeratorModerator

11,162
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Nov 17, 2011
You'll need more knowledge than you obviously have to build a defibrillator.
This thread is imho against our forum policy and I will close it.

Sorry.