The UPS-18650-NS boards arrived from OSH Park on Saturday. By Sunday afternoon I had one of them populated and working. ( I ran out of 3.5mm terminal blocks so that will be the last board built until I get a fresh supply from China.) The polyimide stencil helped to get the solder paste aligned properly on the board, but it was a bit thick and I had to take a pin between the pads of the DFN and MSOP-10 footprints to prevent solder shorts. No shorts this time -- I'm amazed that the DFN package isn't prone to shorts given the pad spacings. If I get another stencil for these small pad footprints I will try the 3mil thickness...

Measured 30µA from the battery terminals with no voltage applied to VOUT. That's a bit higher than the 14500 design but shouldn't matter much with this larger battery. With VOUT = 5.25V, I measured 125µA into BAT, which is pretty close to what I was shooting for. I unplugged the VOUT source and trimmed the open circuit voltage at VOUT to 5.00V.

Next, I inserted a 18650 battery into the battery holder -- it seemed a bit loose so I had to bend the spring clips out a bit. When I plugged the wall wart into the microUSB jack and the plugged the wall wart into the wall socket the battery began to charge. So far so good.

At this point I was confident that the boost converter was working properly so I connected the UPS to my Raspberry Pi 2B and waited until that battery was fully charged to 4V. Then unplugged the wall wart and timed the UPS until it gave up when the battery voltage dropped below 3.0V -- 4 hours 1 minute.

I then disconnected the RPi, recharged the battery back to 4.0V, and attached a 2.5Ω load. This time the UPS lasted 36 minutes 5 seconds, from 4.0V to 3.0V. The output voltage dropped a bit, from 4.96V @ VBAT=4V to 4.94V @ VBAT=3V, but still very good line/load regulation. At the end of the test both the board and the battery were not very hot to the touch -- I estimate less than 15°C rise in temperature, which is fantastic. I measured the approximate time to recharge the battery from about 3.2V back to 4.0V -- about 5 hours, which is consistent with the 0.5A charge current and a 2500mAh Li-Ion battery.

I don't expect to perform much additional testing. The design is very similar to the 14500 design, but with a larger battery. So this prototype will be installed into to my seismometer system in the near future. I need to clean up and finish the powerfail code before that happens.