As an engineer I would guess that recharging the battery will take a long time. It might store energy and deliver it but the self charging aspects would seem to take a lot longer to recharge than just a typical Li-ion type.
Some physicist type can probably figure it out basedon the radioactive decay and how the battery is supposed to work in regards to actual self recharging.
Until NDB demonstrates a usable prototype and shows how it rechages in only a few hours like the Li-ion type I remain skeptical of the actual usefulness of such a design.
This kind of reinforces something I learned a long time ago, Scientists find and study some interesting phenomena, but an engineer has to actually come up with a useful and producible device that people are willing to buy.