Aren't alpha particles those with more penetrating power? That's why glow rings are safe, because the beta particles are completely absorbed by the phosphor material?
The only problem I can see with the atomic battery is the use of moving parts. The fuel source may be good for quite a few years, but the moving parts may need periodic maintainence.
Can't wait for that small multi-source fuel cell. That is one of the main points stunting the widespread use of fuel cells. The most efficient of them is apparently the proton exchange membrane (PEM) fuel cell. Very efficient but uses hydrogen and is quite large. To use other fuels, it requires a reformer which detracts from its efficiency and increases its size.