When our home is not using all of the solar electricity it is producing, say on a sunny day, batteries store the energy for future use. They are very similar in composition to ordinary car batteries, but their electrical capacities are much higher. A typical car battery is rated for 12 volts, and usually holds 40 amp-hours of electricity. Maryland's home features 40 East Penn Deka S8D SLD G LTP batteries, each rated to hold 265 amp-hours at 12 volts.

An "amp-hour" is a unit used to describe how much electricty is held in a battery. One amp-hour means that one ampere of current can be drawn for one hour before the battery is dead. This is approximately the amount of electricity that a 120 watt lightbulb would draw in one hour in a typical home, from a standard 120 volt electrical outlet. To put this in perspective, one of the batteries in the LEAFHouse could power 265 light bulbs for one hour, or one light bulb for 265 hours. This is in the ideal case, however, discharging a battery to zero capacity can damage the battery, and the charge controllers prevent this from happening.

All of this battery capacity is necessary because every 2007 Solar Decathlon home is self-sufficient, and does not receive any grid electricity. Therefore, each home must have an electrical storage mechanism capable of powering the home for several days with very little sunlight.