I have written this information to give a better understanding on deep cycle batteries. I am by no means an expert. I have gathered information from other web sites dedicated to batteries and have attempted to reassemble some of that information here. Any comments, expert advice, suggestions and or corrections would be greatly appreciated!

The DEEP Cycle Battery

What is it?

How to KILL it.

How to make it LIVE along time.

CAUTION: BATTERIES PRODUCE EXPLOSIVE GASSES  WHEN CHARGED OR UNDER HEAVY LOADS. A SPARK FROM ATTACHING JUMPER CABLES CAN IGNITE THESE EXPLOSIVE GASSES CAUSING SEVERE INJURY. ALWAYS ATTACH THE POSITIVE LEAD FIRST THEN THE NEGATIVE LEAD  AN ENGINE PART AWAY FROM THE BATTERY.

What is the differences between a Deep cycle battery and a Starting battery?

Starting battery.

A starting battery is used for starting your engine, running the headlights and ignition and a few other items. Engine starters need a very large starting current for a very short time. Automotive batteries will generally fail after 30-150 deep cycles if deep cycled, while they may last for thousands of cycles in normal starting use (2-5% discharge). Starting batteries have a great number of thin plates giving a maximum surface area. The battery plates are composed of a Lead "sponge", similar in appearance to a very fine foam sponge giving the battery plates a very large surface area, but if deep cycled, this sponge will quickly be consumed and fall to the bottom of the cells. A starting battery can give higher amperage output than a deep cycle battery but only for a short time, such as when starting your car.

The Deep Cycle Battery

Deep cycle batteries are designed to be discharged down to 80% many times over and over. They have much thicker plates. The major difference between a true deep cycle battery and others is that the plates are solid lead plates, not the sponge type. It is often if not always impossible to tell if you are buying a true deep cycle battery as some that are called deep cycle actually have sponge type plates.

The Marine Battery

The marine battery is often confused with the true deep cycle battery. Most Marine batteries are actually a Hybrid. The plates may be composed of Lead sponge, but it is coarser and heavier than that used in starting batteries. The hybrid marine battery should never be discharged more than 50%.

How to kill the deep cycle battery.

Killing the Deep cycle battery is easy. Just let it sit and do not keep it charged. That's what happens to most of them. Our RV sits for a few weeks or months with out any charge being applied to the battery. During the normal discharge process, soft lead sulfate crystals are formed in the pores and on the surfaces of the positive and negative plates inside a lead-acid battery. When a battery is left in a discharged condition, continually undercharged, or the electrolyte level is below the top of the plates, some of the soft lead sulfate re-crystallizes into hard lead sulfate. It cannot be reconverted during subsequent recharging. This creation of hard crystals is commonly called "lead sulfation". It accounts for approximately 85% of the deep cycle lead-acid battery failures. The longer sulfation occurs, the larger and harder the lead sulfate crystals become.

Another way to kill it is to use a bad charger or overcharging. Cheap, unregulated trickle or manual two stage battery chargers can overcharge your battery because they can "decompose" the water out of the electrolyte by electrolysis.

How to keep them alive!

Deep cycle batteries should be recharged every day they are used.

On their days off they should be charged on a regular basis and kept at 100% charge. Solar battery charger maintainers do a good job of keeping the battery at full charge.

Make sure the water or electrolyte is above the plates. Even the maintenance free and sealed batteries will drop in level due to over charging and or high heat.

The chart below shows the charge in a battery and its associated voltage.

Battery Types