If you purchased the rechargeable battery packs, they will need charged before installation and periodically afterwards (see chart below)

Estimated battery life before recharging

0 - 3,600 ~ 12 months
3,600 - 7,200 ~ 6 - 12 months
> 7,200 ~ 6 months 

Sizes are square inches

to charge the battery pack, simply remove the battery pack from the installation brackets, then plug one end of the charger into the battery pack, and the other end into the outlet. 

The charger LED will turn solid green when complete.