A4 is missing. Looks like an important test point is MIA. Am I missing the point here or what?
Look at it this way. You need only to monitor the Li-ion battery voltage as it is in use and is being charged by a solar cell array. You might make and transmit or store a voltage reading every time the GPS transmitter is operating. Estimate the size of the solar cell array and let your instrument run around in the sun for a day or week or a month. The instrumentation you are powering will either drain the battery down faster than it can be charged, or you have the possibility that the solar cell array is getting enough sun and big enough and is keeping the Li-ion battery near full charge on the average. If you need more solar panel power then boost the solar cell size, or else you might want to make is smaller to keep your instrument in business with a smaller footprint, but consider also the cloudiness of the weather in situ.
With a gain of 33, 1 amp across a .1-ohm resistor would give 3.3V. Ok, so you are using a 3.3V MCU/reference for your A2D and you would get 1024 counts for 1Amp or 1.024 counts/mA...close to what you say.