This update goes over my latest research with the BoostPack auto battery replacement project. BoostPacks are now for sale on eBay for $100-$200 Buy It Now. Coupled with a small solar panel my setup has been working flawlessly.
Actually, the solar panel is a 1.8 watt panel:
Untested eBay capacitor packs:
15V 233F US $118.00
15V 380F US $165.00