|Mine will have Anderson PP instead of an auto-type DC plug|
I've just ordered the ingredients for a new project for the year - a Byonics Micro-Trak RTG FA. This is a complete 10-watt APRS tracker in a plug-n-play package.
I've dabbled in APRS before using cobbled-together components from a variety of manufacturers and it resulted in a spaghetti mix of cables, wires, adapters, etc that didn't lend themselves to being easily moved from one vehicle to another. This set-up is compact enough to be used in a car one minute and on a motorcycle the next.
It will likely see use in both of those applications but I also want to see if it is sized (electrically speaking) to a 20-watt solar cell I have along with a 22AH AGM battery. The purpose of that would be to have it installed on our travel trailer so that family & friends could see where we are. Last year's motorcycle trip with a satellite tracker for safety proved informative and useful but costs $30/month for the service. APRS will do the same thing (in most locations) for free.
Determining the power requirements for such a device is almost impossible. Or at least impossibly tedious since the duty cycle is variable. Once I settle on a transmission rate, the plan is to set it up as if I were on the road and let it do its thing while an inline power meter records all the pertinent power info.