My latest experiments involves attempting to power a Raspberry Pi using rechargeable AA batteries. I wanted to see if I could successfully run Raspbian with the standard peripherals using only a pack of four AA batteries and a modified micro USB cable, without any regulators.
The Raspberry Pi is built to run on 5V with a tolerance of ±5%, or a range of 4.75 – 5.25 V. The total voltage of your average AA is 1.5 V, so a total of four standard non-rechargeable AAs adds up to 6V, which is too much for the Pi without using a 5V regulator. However, NiMH AA batteries typically have a voltage of 1.2V, so four of them adds up to 4.8V, which is in the Pi’s operating range.
Although the rechargeable AAs I have were rated for 1.2V, they actually ended up being 1.3V when charged, so that put it at 5.1V, still within the Pi’s operating range.
The funnest part of this whole experiment was modding the micro USB cable. I cut off the cable from an old wall charger and stripped the wires. Unlike a regular micro-to-standard A cable, which has white and green data lines plus the red Vcc and black GND, a micro USB charger only has the black and red because obviously you can’t transfer data from the wall to a device.
I first set up my Raspberry Pi Model B+ with Raspbian with the standard mouse, keyboard, and monitor, and set up the rechargeable batteries. As soon as I plugged it in, it immediately entered the endless reboot cycle, and didn’t end up completely booting at all.
The next test was with my Raspberry Pi Model B. Again with the same peripherals and Raspbian image, I plugged in the batteries, with a little more success. The Model B booted successfully, and I got it logged into the desktop. I left it alone to see how long the Pi could be sustained. Exactly 15 minutes later, the Pi entered the reboot cycle.
So powering the Raspberry Pi models B and B+ wasn’t too successful. Only the model B was able to properly boot and it only ended up lasting 15 minutes, and if I had been running some software or circuits, it probably would have lasted much less.
I might try this test with regular batteries and a 5V regulator to see if the results change. If I were using a model A or A+ Raspberry Pi I would probably have better results because those models have less power requirements. The overall purpose of this experiment was to see if I could cheaply power my Pi using only batteries with no external circuitry.
So the results are:
- Raspberry Pi Model B+…Failure, failed to successfully boot
- Raspberry Pi Model B…Success, booted and stayed on for 15 minutes
Please note that if you try to power your Pi with batteries, be aware of the voltages you’re using. While the Pi might be able to handle 6V input, peripherals like mice and keyboards, which directly receive the Pi’s input voltage, can’t.