At the end of my previous blog post, I mentioned that I was going to test the large pack to see if it was suitable as an uninterruptable power supply (UPS). Since it can be charged while being used, it seemed reasonable to see if it works for this function.
Three days testing
So I decided to put it on test for three days. Those three days ended at 9 am this morning, although I’ve still left it running. The pack has been powering the Pi, while the pack itself is connected to my 1 Amp Nokia charger. The charge indication light has been flashing, the whole time, to indicate charging in progress.
But what about interruptions?
Four times during the test period, I’ve either pulled out the charger from the mains, or pulled the micro USB charge lead from the battery pack. All four times, the Pi has remained up and running. I logged in after each time to check.
Each time I’ve done this, all three ‘charge state’ leds on the battery pack are lit, indicating fully charged.
One further test to do
I want to simulate a long power outage of, say, three hours. This will enable us to see whether the pack will be able to recharge properly whilst still powering the Pi. I expect it will, but we’ll find out tomorrow.
If it passes that test, it can be used as a UPS (see warning below).
Update: It passed. I unplugged the charger for three hours this afternoon to simulate a long power outage. Checking on it a few hours after plugging the charger back in and it’s fully recharged the pack.
That’s not a recommendation though
A warning though. Just because it works, doesn’t necessarily mean it’s a good idea. The life of the pack may be drastically reduced by doing this. Lithium batteries are delicate and don’t like being float-charged.* The device is not sold as a UPS. You do this at your own risk.
But the fact is, that, because it works, you are free to make that choice and take that risk. I don’t need a UPS on any of my Pis, so I won’t be doing it. I tested it for fun and science.
But I’m not saying don’t do it either. I’m saying know what you’re doing and make an informed choice.
* It’s been pointed out to me that technically we’re not float charging. But being on constant charge (even though it cuts off when full), we are no doubt using up cycles of the battery’s life. Also, lithium polymer batteries lose capacity with age a lot faster if kept fully charged.