So OK hows a deep cycle battery different than any other battery?
The main difference is that a deep cycle battery is designed so that it can be almost fully discharged and recharged multiple times, and is not as concerned with “cranking amps” as a normal car battery.
Deep cycle batteries are normally used in boats, RV’s and industrial applications where there is not usually an alternator to constantly recharge the battery while it’s in use.
Batteries are lead plates in acid, basically. For the same amount of lead, you can either make your plates long and skinny or short and fat. How much instant current you can get out of the battery depends on the surface area of the plates, so long and skinny will put out more current than short and fat plates. On the other hand, how long the battery lasts depends on the thickness of the plates, so short and fat lasts longer than long and skinny. Car batteries are long and skinny. Deep cyle batteries are short and fat.
From a practical standpoint, it means that for the same amount of lead, a car battery can put out more cranking amps to start an engine, but goes dead faster than a deep cycle battery. A deep cycle battery can’t put out as many amps, but lasts longer, which is what you typically need in a boat because you often shut the engine off and run on battery power.
One other advantage of deep cycles is that with short plates they allow more space at the bottom of the battery case for collection of sulfate. As batterys are charged and discharged sulfate accumalate on the plates, during intense recharge the sulfates can be shed from the plates and settle on the bottom. Do this too many times with a Starting battery that has long skinny plates and you get a dead short right across the bottom, with fat short plates there is more space for the sulfates to occupy, giving you more discharge / recharge cycles