Short update: Thanks to home projects I hadn't met my goal of completing this one, but progress has been made!

I've decrypted enough information to at least get the core necessities; voltage, amperage and temperature. At this point I'm working on formatting information for the LCD, primarily trying to come up with icons so I can manage the limited space better.

While an 8 mHz microcontroller is doing the job, 16 mHz would be so much better! Since I'm using softwareserial to talk to the LCD (so hardware serial can be left open for debugging) I was running into problems with not being able to keep the overhead low enough that it still caught every bit. Ultimately I had to increase complexity in the code a bit by making the MCU update only portions of calculations and the LCD at a time rather than doing everything at once. This seems to have resolved the problem.

Had I not been using parts I had laying around, a 16 mHz MCU would have been my first choice.

Next up will be focusing on features such as turning off the LCD backlight when there is no solar power to help conserve energy as well as decided how to handle the amp-hour counter; I've yet to decide if I should keep a life-time counter or have it reset at night and only keep track of daily counts.