A ZEBRA battery needs a minimum temperature to operate. That is because only then the ions move freely enough.
The electro-chemical reaction is as follows:
$$NiCl_2 + 2Na \longrightarrow Ni + 2NaCl + e$$
So what if I would cool a charged battery down to room temperature?
Since the one electrode will still consist of $NiCl_2$ there should be charge "frozen".