A4: First, figure out how much power you’ll need during 
a complete power outage, and estimate how long the outage could last. Multiply the outage duration (hours) 
by the total power consumption of your devices (watts) 
to get the required total battery capacity (watt-hours).
Then, divide this number by the capacity of one server rack battery (5,120Wh) to get the number of batteries needed.