Our SAR team does some stuff in national parks and want to build a small self contained APRS digi. I am using the argent board but a mobile is killing battery life and I really don't need 90% of the features. Also size is a concern. Really want all of this in a small box with a small battery.
Several years ago, I built a portable digipeater for use at a 3-day orienteering event being held in a national forest in southern Indiana in January (approx. 30 deg F during the day, 10 deg F at night). The hardware consisted of an Alinco DR-135T mobile radio set to operate at low power (5 watts), an Argent Data Tracker2, and a gel cell battery of the size used in motorized wheel chairs. Everything was packaged in a small, hard-sided
cooler. The package was carried to the top of a fire tower in the middle of the forest. The antenna was a quarter-wave whip on a mag-mount stuck to one of the ribs of the tower.
This digipeater functioned well and still had battery power remaining after three days. I'm not well-versed in solar power, but it seems that a sufficiently-sized solar panel and a solar battery tender would keep the battery charged.
You say that the mobile is killing battery life. Are you running the mobile at high power? Do you find that it's necessary to run high power for the digi to give the performance you want?
You say that the "argent board" has more features than you need. I assume you are talking about an Argent Data device. Which model? OpenTracker? Tracker2? Tracker3? One of the micro or mini models? Yes, the Argent Data have lots of features. It's been my experience with APRS devices that the "dumb trackers" can send APRS position reports, but they don't have the horsepower or features to act as digipeaters. So, you are forced to buy devices with lots of features in order to get the feature, digipeating, that you want.