For two years I've been running your solar weather station using two 6600 mAh Lithium Ion batteries wired in parallel. I made sure they were fully charged when I wired them up. I also have 5 of your solar panels attached. The reason I have the extra capacity is because of trees and lack of lots of clear days. Recently I noticed that my system was randomly shutting down the CPU. I disconnected my watch dog timer and have set the software battery voltage low check to 3.5 volts. The system was still powering off the pi zero at about 3.7 to 3.8 volts. The only thing I can think of is that my batteries are not holding a good charge. My solar panels have what looks like oxidation on the front. The panels still put out over 3 volts when under a desk lamp. They may not be as efficient as they once were, but I feel that they are working ok. I make sure that the system battery voltage starts out at 4.2 volts when I disconnect my house power adapter. I then let the system run off battery power without solar panels and watch the voltage drop. Multiple tests have shown that battery voltage never drops close to 3.5 volts before the Pi is powered off.
My question is simple. Is there any way to easily test the capacity of my batteries?
The software battery shutoff is one way that the Pi will shutdown, but not the only way.
When you say the Pi is shutdown, is it the USB PowerControl shutting it down (the voltage looks right for that)? The USB PowerControl is set to shutdown about 3.7 or so and startup at about 3.9 or so. Hysterisis so you don't ping pong your Raspberry Pi into SD Card Death.
Might be that your batteries are not holding a charge. You can hookup a 10W resistor to the batteries and measure the voltage to see if that is the problem.
2 Years is a good life span for LiPo batteries, especially if they get cold.
BP I'm assuming that the USB PowerControl is shutting down the system. The Pi shows no green LED or any other sign of activity (normally green light blinking most of the time). The rest of the components have the red LED lights on. I have a software log to the SQL database that shows when I shut the system off at low voltage. I thought the USB PowerControl shutdown the system when the voltage was just below 3.5 volts. That was the voltage I had the software check for and then do an orderly shutdown. With the flat discharge curve, every .1 of a volt matters! I'm in Maryland so the batteries do get below freezing in winter. I'll just buy new batteries. Thank for getting back to me. CME