How to Use the Home Battery Storage Calculator
Whether you're pairing a battery with rooftop solar or just want backup power for outages, it can be hard to know what capacity to buy. Enter your daily power use, how many days you want to cover, and your battery's depth of discharge, and this calculator instantly returns the capacity you need.
Depth of discharge (DoD) is the percentage of a fully charged battery you can actually use before recharging. Draining a battery to 100% shortens its lifespan dramatically, so manufacturers recommend using only a portion of total capacity. Lithium iron phosphate (LFP) batteries, now common in home storage systems, often support around 90% DoD or more.
Required capacity is calculated as daily power use × backup days, divided by the usable DoD fraction. For example, a household using 10kWh per day that wants 1 day of backup from a 90% DoD battery needs about 11.1kWh of capacity. Homes in areas with reliable grid power often plan for just 1 day, while homes in hurricane-prone or storm-heavy regions frequently size up to 2-3 days for extra margin.
Frequently Asked Questions
DoD is the percentage of a battery's capacity you can actually use before recharging. Modern lithium iron phosphate (LFP) batteries commonly used at home typically allow around 90% or more.
A typical home targets 1 day, while areas prone to hurricanes, ice storms, or slow utility restoration often plan for 2-3 days of extra margin.