In my previous battery tests I’ve stuck to AA batteries. Mainly because I’ve got lots of them and I like their versatility. Recently I decided to buy a portable Li-on battery pack designed for recharging mobile phones and tablets while on the move. Given I could use it for portable Raspberry Pi projects and charging mobile devices it seemed like a good thing to buy.

So I picked one from eBay. If you are going to have one you might as well have a big one so I opted for a device with a stated capacity of 12000mAh. It has two USB ports which support charging currents of 1A and 2A although the total current from both ports can not exceed 2A.

Test Setup

So I setup a Pi using the same setup as I used before.

Predicted Battery Stamina

The stated battery capacity of many Power Banks is a bit confusing. They rarely confirm at what voltage the capacity relates to. Is it the 5V output or the internal 3.7V of the Li-on battery cells? Thanks to a comment by Ben Friesen (see below) I have revised this article to assume the stated capacity is measured at 3.7V. The energy in the battery pack can then be calculated using :

`E = 12000mAh x 3.7V / 1000 = 44.4Wh (watt hours)`

This compares to a typical 6 AA battery pack :

`E = 2600mAh x 8V / 1000 = 20.8Wh`

The AA battery packs gave 8 to 9 hours with 20.8Wh so I would expect 44.4Wh to give 17 to  19 hours.

Results

The total time I measured was : 18 hours 40 minutes.

That is a total of 1120 minutes.

Conclusions

After revising my estimate using 3.7V as the internal battery voltage this is exactly as expected.

Overall I am pleased with the results and this has to be the easiest way to power a Pi when you can’t plug it into the mains. I’m a fan of AA batteries but if you need 10+ hours out of your Pi then you can’t beat the density of a Li-on battery pack.

Photos

Here are some photos I took during the test showing the size of the Power Bank compared to the Pi :

I’ve included a photo of the packaging in the collection of photos as it contains some entertaining statements such as “Get rid of kids”.

Note : The eBay description stated the battery could be charged via MicroUSB but the device is actually fitted with a MiniUSB port. This is a huge difference and something I pointed out to the seller. I didn’t mind as I have Mini and Micro USB chargers but I did expect the description to be updated for the sake of other buyers. The seller hasn’t bothered to change the description which is why I’m not going to bother giving him a free advert here. Before assuming you can charge the battery pack with MicroUSB get the seller to confirm it via an eBay message.

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1. “This product should be keep out of children.”

Quite right too. Superb Chinglish. Nice review Matt.

2. The stated capacity on lithium ion batteries is not for 5 volts. Lithium ion batteries have a output voltage of 3.7 volts and from there the voltage is raised to 5 volts. This means that the battery actually has a capacity of 44.4Wh. This brings the battery life right into line with capacity.

3. Recently I tested that powerbank.
My result is 2.5 hours @ 700mA load. (less than 2000mAh)
Is that device broken?

4. Does this one shut off the outputs when charging like the RAVPower does?

Also, can anyone elaborate on any issue with charging while producing output power? For instance, would a solar panel charging the battery while an Rpi is on the output have any negative effects?

5. I’ve been planning to use my Pi for a 4 day project, I have 2 of these power packs and have been looking at the best way to save power. Outside of hard modding (which I’m not against, but I don’t have enough time left before the project that I can buy a new Pi if I mess it up) seems to be disabling the LAN port (source: http://raspberrypi.stackexchange.com/questions/8498/disable-lan9512) to save around ~200mA of power. This puts it almost online with the Model A which is apparently 1/3rd of the power consumption (source: http://www.raspberrypi.org/phpBB3/viewtopic.php?f=29&t=32955).

Going from ~380mA to ~280mA is a roughly an increase of 145% in run time, from ~18h40 to ~26h.

I’m giving it a go this weekend and let you know how it turns out!

6. >> “Does this one shut off the outputs when charging”
Confirmed: Yes, charging stops the output. Bum. Otherwise would be a perfect UPS.
However, within that limitation, it works well.

7. Further info in my experiences with this battery.

I actually have a “2600 mAh” single cell one, as well as the “12000 mAh” 4-cell under discussion. After a couple of days using them, I would have to say their capacity seems WAY WAY below the claims. I have some measured figures for both, after a couple of full charge/discharge cycles.

The “12000” pack:
— Claim = 12000 mAh. Supposedly 44.4 Wh battery storage, as this blog notes.
— Integrated total charge accepted at 5.06V input from empty to full (the current varies, so I kept a log) = 22 Wh.
— Discharged into resistor load. Constant 5.15v output, 510 mA. Total output at 5.15V: 15.1 Wh (34% of claimed capacity).

The small “2600” battery pack:
— Claim = 2600 mAh. Presuming this is at battery 3.7 volts, this represents 9.6 Wh that should be stored.
— Integrated total charge accepted at 5v : 650 mAh. That’s 3.25 Wh I fed in.
— Discharged into resistor load. Constant 5.25v output, 100mA. Total output at 5.25V: 2.34 Wh (24% of claimed capacity).

So, did flattening the packs a couple of times do them instant damage? Or are these things just a long way out of spec? Or am I doing or expecting something wrong? Or what else should I expect at \$5.50 and \$11?

8. Sorry to bother you with a question you may not have an answer for. I have the exact same 12000 mAh Power Bank (at least it looks identical to yours) but it only charges phones. I tried using it with Arduino and Raspberry Pi, the 4 LEDs stay lit for a while and then it turns off. I tried both ports, 2 different cables with no success. Did you ever see something like this? Did you make any mods to yours that made it work or it just worked first try?

Thanks for all your awesome articles!

• Mine worked ok. It didn’t power my HDMIPi as the voltage level wasn’t quite stable enough under load but the normal Pi ran OK.

9. Are you about to charge and power the pi concurrently?

• Some battery packs claim to be able to charge at the same time but it’s hard to determine if this is safe. Or whether it will adversely affect the lifespan of the battery. I tend to assume that they aren’t designed for it so probably not a good idea.