To restate the rule, in case someone can't find it:
If it's 100Wh or below, you can pack it without prior approval. From 100Wh to 160Wh, you need the airline's approval, but you can't carry more than two power packs. Power packs over 160Wh are forbidden.
You'll have to convert mAh to Wh for your particular battery, since it depends on the voltage.
You also can't use your power pack on board.