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My thesis group is building a project involving the Raspberry Pi.

It is known that the RPi runs around an average of 700mA of current and my project would probably need a little over 1A of current due to attached components.

I am looking into cellphone batteries for the supply because they are already compact and lightweight, since our project needs to be portable. So i am asking those who have already tried using cellphone batts for their projects. Will it be able to supply the raspberry pi efficiently if i use a 5v regulating circuit? and will the batteries be able to supply the needed current mentioned above?

Oh and i would also like to know what kind of setup you used and how long your project lasted running. :)

These are the components attached to the RPi that will probably consume relevant power:

  • GPS shield
  • Ultrasonic sensors (2 or more)

*The RPi will also be installed with text to speech software, so it will be playing audio every now and then while keeping the ultrasonic and the gps components running the whole time.

I will look into everyone's answers. I will update as soon as something works. :) Thanks!

EDIT: Finally ended up using a 10k mAh power bank due to the ease of charging and connecting :)

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    \$\begingroup\$ Have you considered usb battery packs? They provide a charger, regulator, battery and casing in a neat package. \$\endgroup\$
    – Passerby
    Commented Mar 4, 2015 at 16:06
  • \$\begingroup\$ How much battery life do you need? Are you saying your average is around 1A@5V? That is 5W. You should research the cell phone battery capacity. I would guess some of the bigger smart phones may be around 10Wh, meaning 2 hours of battery life. I think any lithium ion battery pack will be OK with a C/2 discharge rate (two hours battery life). You can also consider using 18650 lithium ion cells. Either one cell (around 11 Wh) or 2cells (for 22 Wh). \$\endgroup\$
    – user57037
    Commented Mar 5, 2015 at 5:37
  • \$\begingroup\$ Do NOT attempt to charge a cell-phone battery without using a charger (or charger circuit) designed specifically for Li-Poly batteries. Charging a cell-phone battery directly off of 5v will most likely result in a fire. \$\endgroup\$
    – tcrosley
    Commented Mar 5, 2015 at 7:25
  • \$\begingroup\$ @tcrosley, I agree. But did someone suggest to do that? Or are you just trying to head off a potential danger? \$\endgroup\$
    – user57037
    Commented Mar 6, 2015 at 0:05
  • \$\begingroup\$ @mkeith Both actually. The post said "if i use a 5v regulating circuit", and I was afraid they might attempt to directly charge the battery from that. But it is a general warning also -- even of one had a voltage rail equal to the maximum charge voltage (4.2v) for a cellphone battery, one should not connect that to the battery; you have to use a special Li-Poly charger IC. \$\endgroup\$
    – tcrosley
    Commented Mar 6, 2015 at 0:22

2 Answers 2

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I suggest taking a look at RC batteries used by RC planes, boats, cars and drones. They're the same thing as cell phone batteries only cheaper, smaller and lighter. And are available up to sizes that wouldn't fit even a laptop much less mobile phones (and down to sizes as small as you little finger).

Google "lipo battery" and the top 5 results will lead you to an online store that sells them. You can buy them from Amazon if you want if you don't mind paying typically 50% more than what hobby shops sell them for.

Additional Info:

RC batteries typically can source much more current compared to phone batteries. A typical park flying plane (wingspan of around 1m or between 36 and 42 inches) usually consumes around 20A of current. Though it's not uncommon to see people fly really fast planes that can easily slurp up to 40A. Big planes that need special flying fields to take off from consume anywhere from 50A up to more than 100A. Given this, I don't think the current ratings of these batteries matter much for your application as even the lowest rating will be overkill.

Current ratings for batteries are usually given as C-ratings. 1C is defined as the battery being drained in 1 hour. 2C means you can drain the battery in 30 minutes without excessively damaging it. Batteries are typically rated as 10C or more.

How to calculate maximum current source is simple: take the batteries' amp-hours (convert milliamp to amp) then multiply by the C rating. For example, a 2200mAH 20C battery can source 2.2A * 20 = 44A.

As for capacity. Again, it depends on the size of your aircraft/boat/car. The smallest battery you can get is around 120mAH and the largest is around 100000mAH. The most common RC battery is probably the 2200mAH 3-cell (12V) battery.

If you're going to be buying RC batteries, ask for SBEC (or S-BEC) as well. They're cheap switch-mode power supplies and are typically more than 90% efficient. Much cheaper than buying industrial grade DC/DC converters and easier than building your own buck converter. Most output 5V but some have jumpers allowing you to select between 5V and 6V output.

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  • \$\begingroup\$ hmmm what is the safest maximum current i can draw out of those? and would you happen to know a common rc batt mAh? \$\endgroup\$
    – Alexander Sabiona
    Commented Mar 9, 2015 at 8:36
  • \$\begingroup\$ Typically around 5x more current than phone batteries. They're rated with C ratings where 1C is defined as draining the battery in 1 hour (2C means draining it in 30 minutes, 3C = 20 minutes etc.). I'll add more info in my answer. \$\endgroup\$
    – slebetman
    Commented Mar 9, 2015 at 8:49
  • \$\begingroup\$ Hmmmm the numbers look promising, i'm just curious and i know it's a stupid question but will it run fine for the raspberry pi? since this RC batt is used for analog applications(motor) obviously, will it be a problem with the RPi since it's digital? \$\endgroup\$
    – Alexander Sabiona
    Commented Mar 9, 2015 at 9:40
  • \$\begingroup\$ There's no such thing as an analog or digital battery. Voltage is voltage and chemistry is chemistry. What makes it suitable for driving large motors is it's high current capability. Just make sure you boost or regulate it to 5V since lipos don't come in 5V. I'd personally recommend getting a 2-cell (8V) battery and use a switch-mode power supply to convert it to 5V. Mainly because they're easier to find compared to voltage boosters. \$\endgroup\$
    – slebetman
    Commented Mar 9, 2015 at 23:47
  • \$\begingroup\$ Yeah i know there's no analog/digital batt, but that batt is used for strong motors that pull a lot of current. So it will be fine as long as i use a regulating circuit? no difference? Sorry, my knowledge about batteries is minimal. I just know the basics hahaha, thank you for being patient with me. \$\endgroup\$
    – Alexander Sabiona
    Commented Mar 10, 2015 at 0:38
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I would recommend against using cell phone batteries for your project. You simply require too much current. For example the iPhone 5 battery has a capacity of 1510 mAh, and would only last 1.5 hours max in your device. In fact the 1510 is at the 3.7 nominal volts that lithium batteries run at. You will get less time out of the battery as you lose some capacity to the conversion up to 5 volts. Also, these smart phone batteries were designed to be discharged over an 8-10 hour time frame and may not last nearly as long (in terms of number of charge/discharge cycles before it dies) when pushed so hard in your device.

You might be better off looking at the batteries designed for smaller tablets. They tend to have a capacity of closer to 4500 mAh.

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  • \$\begingroup\$ Very useful information Filek :) thank you! Hmmm, i will look into tablet batts, i have never considered thpse. Although, i'm worried about the size, hopefully there are compact ones. We'll see. Oh and 4.5 Ah looks good though. If it pulls out too much current out of the cell phone batt hmmm then.. will putting it in parallel help lessen the current stress on each batt? and this will help increase run time as well right? \$\endgroup\$
    – Alexander Sabiona
    Commented Mar 9, 2015 at 1:33
  • \$\begingroup\$ Yes, adding the cell phone batteries in parallel would add to the capacity and decrease the stress on them, but since they are the same technology as the tablet batteries, they will end up being a similar volume and weight after adding them together. \$\endgroup\$
    – Filek
    Commented Mar 9, 2015 at 6:21
  • \$\begingroup\$ ahhh, i see. thank you Filek :) i will try to look into both cell phone and tablet batts. I am considering cell batts because i think they are easier to get. \$\endgroup\$
    – Alexander Sabiona
    Commented Mar 9, 2015 at 6:48
  • \$\begingroup\$ Good point. In the end go for the easiest and cheapest. \$\endgroup\$
    – Filek
    Commented Mar 10, 2015 at 6:03

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