Explaining Computers' Christopher Barnatt has opted for something a little beefier than your usual lithium-ion battery pack to power his Raspberry Pi single-board computer: a 12V sealed lead-acid battery.
"12V batteries are very common indeed," Barnatt explains by way of introducing the somewhat unusual choice of power source for a range of Raspberry Pi single-board computers on test in his latest video, "because they're used in cars and boats and things like that, and therefore over the years many people have asked me about running a Raspberry Pi on a battery like this.
"To make it work we need to convert the 12V power we get out of the battery down to 5V for a Raspberry Pi, and here I'm going to do that using this which is a packet of magic beans — no it isn't a packet of magic beans it's a buck converter. "It's rated at 5A and it accepts 12V input at this end using either a barrel jack or terminals and it outputs 5V at the other end using either terminals or a Type A USB connector. The big advantage of using a buck converter like this to do our power conversion is that buck converters are very efficient indeed: It's about 90 percent efficient when you convert power from one voltage to the other."
Efficiency is one thing, but there are other issues at play which could limit the usable output of the battery — as low, Barnatt warns, as 50 percent of stated capacity, though typically only in high-current operation. The only way to find out what that means for a relatively low-current Raspberry Pi 4 Model B single-board computer: Benchmarking, with the system set up to flash an LED and continuously write to a file to see how long the battery can keep up.
"The [Raspberry] Pi 4 ran for an extraordinary amount of time on the lead-acid battery," Barnatt found. "There we are: A total uptime of 40.1 hours, if we round to one decimal place — which is massively more than I anticipated, over twice what I calculated. [Testing] the Raspberry Pi 3 A Plus on the lead-acid battery, it has run a considerable period of time: It's run just over three days, 72.1 hours. The Raspberry Pi Zero's lead-acid battery test ran for more than a week - it wouldn't complete in a whole week. 187 hours."
By contrast, a commercial 5V 10Ah battery pack was tested and managed just 15 hours for the Raspberry Pi 4 Model B, 27.7 hours for the Raspberry Pi 3 Model A Plus, and 58.5 hours for the Raspberry Pi Zero — though, admittedly, the commercial power pack is somewhat lighter and more portable than the lead-acid battery.
The full video is now available on the Explaining Computers YouTube channel.