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Like many other Raspberry Pi Zero users out there, I have decided to make a portable retro gaming handheld. One of the larger concerns for me when it comes to this is battery life. The Zero has very little power consumption, although I would love to know if anyone could give me an idea of how long the Pi would last while plugged in with an Adafruit USB Audio Adapter and a 3.5" BW TFT LCD running at 5v, using a 4400mAh lithium polymer battery. If I sound rather noobish - that's because I am :P so please be forgiving if I asked something that may be very simple to answer :D

Thank you so much!

thatoneguy245
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  • You'll find this overview helpful http://raspberrypi.stackexchange.com/a/5034/19949 of course you need to obtain a good estimate of power consumption of the display too. – Ghanima Oct 18 '16 at 07:24
  • Beware I think if you dig into the concept of mAh and the nature of batteries a bit you'll find the rating refers to what the battery delivers at its stated voltage. Although you don't say anything about this, 5V would be unusual; 3.7 V is more normal. When those are used in, e.g., USB power banks, the manufacturers often exploit this by using the mAh rating of the batteries in the pack which are 3.7V stepped up to 5V, and they don't take into account this reduces the number of mAh the pack will actually supply at 5V. – goldilocks Oct 21 '16 at 18:21
  • https://en.wikipedia.org/wiki/Boost_converter#Overview -> "P = VI", and if P stays the same and V increases, then I would go down. A 3.7 V, 1 A device is lower power than a 5 V, 1 A device. To power a 5V, 1A device from a 3.7 V source, that supply must be more than 1A. – goldilocks Oct 21 '16 at 18:33
  • So, that's a ratio of 1.35 and 4400 / 1.35 = 3260. – goldilocks Oct 21 '16 at 18:54
  • The display I am using is designed to run at 12v, but steps down the input voltage to 5v when running, due to it being a car monitor. Because of this, I can solder directly to the pcb and power it via the 5v output from the powerboost. It uses 2 watts. By using the formula A = W/V, i can plug in A = 2/5, giving an amperage of .4A, or 400ma. However, since the display is made to run at 12v and I am running it at 5v, does that essentially mean that the amperage is actually about 40% of that? Or more specifically, about 160ma? – thatoneguy245 Oct 22 '16 at 00:24
  • Here is the display: https://www.amazon.com/BW-3-5-Inch-Monitor-Automobile/dp/B0045IIZKU/ref=sr_1_1?ie=UTF8&qid=1477095906&sr=8-1&keywords=3.5+inch+display – thatoneguy245 Oct 22 '16 at 00:25

3 Answers3

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Similar questions have been asked and answered, you might search for other questions.

Here are a few:

Battery Power Requirements

How long does the RPi last on a battery?

Community
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digitalmint00
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    Hello and welcome. Please note that your post has been flagged by two users for moderator intervention, well, and here is the thing. Whilst this may theoretically answer the question, it would be preferable to include the essential parts of the answer here, and provide the link for reference - or to provide a little context as to why you think the linked answers are of relevance. – Ghanima Oct 18 '16 at 07:34
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    There is another important issue to consider here: duplicate questions. If either of your linked answers (or any other that is not linked for that matter) answers the question then the question itself should be closed as a duplicate of the other. – Ghanima Oct 18 '16 at 07:34
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    ... and with respect to the link-only nature of the answer: we're trying a new policy with regard to informationless link-only answers here. If this post is not edited to contain information that can stand as an answer, however minimal, in 48 hours it will be converted to Community Wiki to simplify having it corrected by the community. We discussed whether this should also be applied to internal links and the consensus is yes, it should. – Ghanima Oct 18 '16 at 07:37
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If you want to evaluate the battery life by yourself, those are the considerations. You must evaluate the mean energy absorbed by Raspberry in your project. You can use a 'USB voltage and current tester' to check current need by your progect. If this value is not constant over the time, you have to do a mean.

The power (or if you prefer, the energy need for 1 second) absorbed by the device, is V*I. V for Raspberry is 5 Volt. Suppose, I = 150 mA so P=5*0,15 = 0.75 W or 750 mW.

Now, if your supply is a battery, I suppose you have a DC/DC converter, to convert the battery voltage to Raspberry's voltage. The converter isn't ideal. A small converter may have a performance of about 90%, so for every watt from Raspberry, you need 1.11W from battery. 10% of energy is wasted as heat on the converter.

In the example 0.75W from Raspberry is 0.75/.9 = 0.83 W from the battery or 0.83 W per second. Your battery with 4,4 Ah (or 4400 mAh) at 3,7 volt (I suppose a lithium battery) store an energy equal to 4,4*3,7*3600 = 58608 joule (we multiply by 3600, the seconds on one hour).

The life of your battery, in seconds, is (energy stored on battery)/( absorbed energy), in our example 58608/.83 = 70612 seconds or 70612/3600=19.6 hours.

Fabrizio Restori
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I did some calculations and research and got at least 22 hours.

According to https://www.raspberrypi.org/forums/viewtopic.php?f=63&t=127210 with a 32GB SD card, composite video and a keyboard, the highest power consumed was 140mA, and with a 4400mAh battery, that's about 22 hours.

Oliver
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