DCDW battery life test enters a 3rd month with over 8v remaining in a 9v generic battery.
Details: actual battery terminal voltage (blue, volts, R axis) measured by DVM, transmit interval (red, sec, L axis) in this config indicates battery health. Note on Jun 27 the battery was accidentally fat probed (shorted out) while measuring voltage. The battery recovered but with unknown loss of capacity.
Actual voltage varies with battery temp as this was in my truck most of the time, getting alternately roasted and cooled every day. The reporting interval for a few days looks like this:
The thin line is the DCDW node reporting interval as seen and logged by Arduino. Sometimes packets are missed due to noise or collision, so this interval appears to jump to multiple times its actual value. Right now a spreadsheet formula in Open Office is correcting for this, which produces the thick line. This same processing might also be done in Arduino sketch before the data is uploaded.
Near 140 hours there is a gap where too many packets were missed for a correction to be applied.
The plot shows a definite daily cycle of about 5% due to wide temperature swings as the 9v battery roasting and cooling inside the truck. Other little wiggles are me driving somewhere or just idling the engine to recharge the truck battery. I run the air conditioner which cools and changes the terminal voltage of the 9v battery.
Aside from the minor variations, over the first 2 months the reporting interval has increased by about 30% while the battery voltage has dropped by about 20%. Plenty good enough to indicate battery health and allow adequate warning for replacement.
Since starting the test I have been on several trips, so far I have managed to lug everything with me on the road and keep it all running more or less continuously. The most difficult thing to keep running is WinDoze on a netbook using an inverter in my truck. Besides occasionally flattening the battery WinDoze sometimes crashes or loses the virtual COM port or the netbook otherwise needs to reboot. Eight spreadsheets of data like this have been recorded spanning the two months with a few small gaps. When the truck battery dies the Arduino does also, so it has been restarted a few times as well. The time column is the Arduino millis() counter, formatted as HH:MM:SS.SSS.
The DCDW node itself has no software and depends only on its 9v battery. It has run continuously without stopping since the end of April.