The newer type of sealed non-spillable maintenance free valve regulated battery uses "Absorbed Glass Mats", or AGM separators between the plates. This is a very fine fiber Boron-Silicate glass mat. These type of batteries have all the advantages of gelled, but can take much more abuse. These are also called "starved electrolyte. Just like the Gel batteries, the AGM Battery will not leak acid if broken.

A gel battery design is typically a modification of the standard lead acid automotive or marine battery. A gelling agent is added to the electrolyte to reduce movement inside the battery case. Many gel batteries also use one way valves in place of open vents, this helps the normal internal gasses to recombine back into water in the battery, reducing gassing. "Gel Cell" batteries are non-spillable even if they are broken. Gel cells must be charged at a lower voltage (C/20) than flooded or AGM to prevent excess gas from damaging the cells. Fast charging them on a conventional automotive charger may be permanently damage a Gel Battery.

Sulfate is the formation or deposit of lead sulfate on the surface and in the pores of the active material of the batteries' lead plates. If the sulfate becomes excessive and forms large crystals on the plates, the battery will not operate efficiently and may not work at all. Common causes of battery sulfate are standing a long time in a discharged condition, operating at excessive temperatures, and prolonged under or over charging.

1. Inadequate first charging or long interruption time of charging;

2. No sufficient charging for long time;

3. No timely recharging after discharge;

4. Often excessive charging or deep discharge with small current;

5. Electrolyte density or temperature is too high so that lead sulfate will form and hard to decompose.

6. Lay the battery aside for a long time and without any regular charging;

7. Electrolyte is not pure and large self-discharge;

8. Internal short-circuit or leakage of electricity caused by the water on the surface of battery.

9. Barely plate partially sulfated because of low Level of internal electrolyte liquid surface.

Advantage: low price: the price of lead acid batteries is just 1/4~1/6 of that of other types of batteries with a lower investment which most users could bear.

Disadvantage: heavy and bulk, low specific energy, strict on charging and discharging.

Lead acid batteries are 100% recyclable. Lead is the most recycled metal in the world today. The plastic containers and covers of old batteries are neutralized, reground and used to the manufacture of new battery cases. The electrolyte can be processed for recycled waste water uses. In some cases, the electrolyte is cleaned and reprocessed and sold as battery grade electrolyte. In other instances, the sulfate content is removed as Ammonia Sulfate and used in fertilizers. The separators are often used as a fuel source for the recycling process.

The most common battery rating is the AMP-HOUR RATING. This is a unit of measurement for battery capacity, obtained by multiplying a current flow in amperes by the time in hours of discharge. (Example: A battery which delivers 5 amperes for 20 hours delivers 5 amperes times 20 hours, or 100 ampere-hours.)

Manufacturers use different discharge periods to yield an different Amp-Hr. Rating for the same capacity batteries, therefore, the Amp-Hr. Rating has little significance unless qualified by the number of hours the battery is discharged. For this reason Amp-Hour Ratings are only a general method of evaluating a battery's capacity for selection purposes. The quality of internal components and technical construction within the battery will generate different desired characteristics without effecting its Amp-Hour Rating. For instance, there are 150 Amp-Hour batteries that will not support an electrical load overnight and if called upon to do so repetitively, will fail early in their life. Conversely, there are 150 Amp-Hour batteries that will operate an electrical load for several days before needing recharging and will do so for years. The following ratings must be examined in order to evaluate and select the proper battery for a specific application: COLD CRANKING AMPERAGE and RESERVE CAPACITY are ratings used by the industry to simplify battery selection.

Reserve capacity is the number of minutes a battery can maintain a useful voltage under a 25 ampere discharge. The higher the minute rating, the greater the battery's ability to run lights, pumps, inverters, and electronics for a longer period before recharging is necessary. The 25 Amp. Reserve Capacity Rating is more realistic than Amp-Hour or CCA as a measurement of capacity for deep cycle service. Batteries promoted on their high Cold Cranking Ratings are easy and inexpensive to build. The market is flooded with them, however their Reserve Capacity, Cycle Life (the number of discharges and charges the battery can deliver) and Service life are poor. Reserve Capacity is difficult and costly to engineer into a battery and requires higher quality cell materials.

One cycle of a battery is a discharge from full charge to full discharge and a return to full charge again. The total number of cycles a battery can perform before failure is called its Cycle Life. Moat battery manufacturers will not discus the Cycle Life of their product. Many advertised Deep Cycle batteries have not been tested, or, which is the case with cranking batteries, were never designed for long Cycle Life .

Discharge efficiency refers to the ratio of actual power to nominal capacity when battery discharges at the ending voltage in certain discharge conditions. It is mainly affected by factors such as discharge rate, environmental temperature, internal resistance. Generally, the higher the rate of discharge is, the lower the discharge efficiency will be; the lower the temperature is, the lower the discharge efficiency will be.

OVERDISCHARGING is a problem which originates from insufficient battery capacity causing the batteries to be overworked. Discharges deeper than 50% (in reality well below 12.0 Volts or 1.200 Specific Gravity) significantly shorten the Cycle Life of a battery without increasing the usable depth of cycle. Infrequent or inadequate recharging can also cause over discharging symptoms called SULFATION. Despite that charging equipment is regulating back properly, over discharging symptoms are displayed as loss of battery capacity and lower than normal specific gravity. Sulfate occurs when sulfur from the electrolyte combines with the lead on the plates and forms lead-sulfate. Once this condition becomes occurs, marine battery chargers will not remove the hardened sulfate. Sulfate can usually be removed by a proper desulfation or equalization charge with external manual battery chargers. To accomplish this task, the flooded plate batteries must be charged at 6 to 10 amps. at 2.4 to 2.5 volts per cell until all cells are gassing freely and their specific gravity returns to their full charge concentration. Sealed AGM batteries should be brought to 2.35 volts per cell and then discharged to 1.75 volts per cell and then this process must be repeated until the capacity returns to the battery. Gel batteries may not recover. In most cases, the battery may be returned to complete its service life.

CHARGING Alternators and float battery chargers including regulated photo voltaic chargers have automatic controls which taper the charge rate as the batteries come up in charge. It should be noted that a decrease to a few amperes while charging does not mean that the batteries have been fully charged. Battery chargers are of three types. There is the manual type, the trickle type, and the automatic switcher type.

Though there is a strict battery selection procedure, after a certain period usage, the non-homogeneity will appear more and more obviously. Meanwhile, charging equipment can’t choose and recongnize the weak battery out, so it is user who can take control of how to keep the equilibrium of battery capacity. User would better test the OCV of every battery regularly or irregularly in the middle and later period of battery pack usage and recharge the battery of lower voltage separately, in order to make the voltage and capacity as the same as other batteries ,  that decrease the difference between the batteries.