Re: fire power
so we are wrapping a small fire bomb in a detonator?
No - there's no mechanism that could cause the ultracapacitor voltage to exceed that of the battery (other than the battery spontaneously developing an internal short-circuit, which is almost certain to result in it catching fire shortly afterwards, ultracapacitor or no)
I am slightly concerned that this device might be useful to a terrorist, i.e. the power surge which it needs to cope with being the power draw of a detonator on a bomb when its timer reaches zero. However, I guess they could buy a separate ultracapacitor, and wire it in parallel with a battery.
Advantage of integrating the battery and ultracapacitor? Packaging, I'd guess. No dead space between two separate components.