The mainstay of renewable energy systems is the deep cycle battery. "Deep
Cycle" is a term used far to often in the wrong situation. Batteries that
are sold as marine/RV deep cycle - in the 24 and 27 series are no more than
slightly modified starting batteries with a different label. These batteries,
as well as any car type starting batteries, including 4D and 8D starting batteries
are simply not suitable for alternative energy applications and will yield unsatisfactory
performance.
A true deep cycle battery, such as a golf cart of forklift batteries are designed
from the ground up for deep cycling applications. This does not mean, however,
you should completely discharge the batteries on a regular basis!