I had a need to log GPS position and vehicle battery voltage, that I met by modifying a KinetaMap (with a little help from Ryan on firmware).
KinetaMAP already logs it’s own LiPo battery using an onboard voltage divider. I cut the trace going to the LiPo and wired an external resistor going to a custom cigarette lighter adaptor to get alternator/car battery voltage. Ryan kindly provided the slightly modified firmware to correctly log my 0-15 volt reading rather than 0-3 volts for the LiPo (Thank you, Ryan!) Other changes particular to my application were:
-replaced the the 900 mah KinetaMap battery with a 3000 mah battery that provided >60hrs runtime (with Bluetooth and accelerometers OFF); this allowed 9-5 data logging 7 days a week (my target)
-modified the cig. lighter plug to act as a switch, powering the KinetaMap (and providing access to the logged voltage) only when plugged into cig. lighter receptacle
-packaged all in a Pelican 1020 box with coiled cable running to the cig. lighter adaptor and KinetaMap LEDs visible through clear top of the case (with a right angle USB plug, a short USB cable fit in the case for dataload and battery recharge)
Previous in-house designs using dual Logomatics (for GPS and voltage) were functional but had higher power consumption and greater size and weight (from batteries), and there was excessive delay if the Logomatic had too many files and wasn’t powered up until engine start.