I was thinking more along the lines of a direct charge device rather than an RTG. Readily available source materials are weak and you really wouldn't want the risk of working with stronger sources anyway however, multiple weak sources charging a capacitor bank to provide a periodic short burst...
I've read about why it would be nearly impossible for an individual to construct a working home built nuclear reactor (of any variety), but I've never understood why a home built nuclear battery couldn't be constructed (think Henry Moseley's work). The size and power output would be impractical...