The secret of battery runtime lies in the capacity. Capacity defines the energy a deep cycle battery can hold. The definition for capacity is usually given in ampere-hours (Ah); it specifies the elapsed time when discharging a battery at a calibrated current to the end-of-discharge voltage. Portable batteries commonly use a one-hour discharge; larger batteries are rated at either a 5 or 20-hour discharge.
  Lead acid batteries come in two basic architectures: deep cycle and starter types. The deep cycle battery is designed for maximum capacity and high cycle count. This is achieved by installing thick lead plates. Typical applications are golf carts, wheelchairs, people movers, scissor lifts and RVs. Starter batteries, in comparison, are made for maximum CCA (cold cranking amp). The battery maker obtains this by adding extra plates to get a large surface area for maximum conductivity. Capacity and deep cycling are less important for automotive because the battery is being recharged while driving. If continuously cycled, the thin lead plates of the starter battery would wear-down rather quickly. As a rule of thumb, the heavier the battery, the more lead it contains and the longer it will last.

An uninterruptible power supply (UPS) is a battery-driven power supply that helps protect electronic equipment from a sudden loss of power. It is especially useful with computers and equipment that could suffer damage in a power outage. In some cases, UPS battery units can be combined with generators to provide power for longer-term outages in larger, corporate environments where downtime could hurt business.

Uninterruptible power supply units are important for certain types of equipment that could be damaged in a power failure. For example, computer servers are typically left running 24 hours a day, as they provide services and files for other computers. A power outage could corrupt the data on a server or make data unavailable to users. In large business environments, networking equipment could also benefit from being on an uninterruptible power supply, as a lack of power to network equipment could prevent communication on the network. In both cases, a, uninterruptible power supply can ensure that the equipment remains operational even if external power was unavailable, as well as reduces the chance that a power outage could corrupt data on a server. In these cases, an appropriate backup power solution is highly recommended.

In other cases, uninterruptible power supplies are less necessary. Individual computers in a home or office likely do not necessarily need backup power. In these instances, while backup power from a UPS could ensure that the computer would be operational during a power outage, it is likely that a lack of power to other devices (such as having no lights or other electrical equipment) would make the backup power less than worthwhile. While a sudden power outage could corrupt data on a computer that was running, regular backups of a home or office PC provide protection against data loss. While uninterruptible power supply units aren't necessary for many PC systems, small units are available for little money and can provide a measure of protection against power failures.

Uninterruptible power supply units come in a variety of capacities and price ranges. Some UPS units are designed to provide enough power to keep computers running just until they can be safely shut down. Others can keep equipment operational for hours. When purchasing a uninterruptible power supply, it is important to consider what equipment must be kept running, as well as for how long. The more devices that are connected to the uninterruptible power supply, the faster a battery-based power supply will drain. Not surprisingly, larger-capacity solutions with longer-term power supplies generally cost more than smaller systems.

The sealed lead-acid battery is designed with a low over-voltage potential to prohibit the battery from reaching its gas-generating state during charge. This prevents water depletion of the sealed system. Consequently, these batteries will never get fully charged and some sulfation will develop over time.
  Finding the ideal charge voltage threshold is critical and any level is a compromise. A voltage limit above 2.40 volts per cell produces good battery performance but shortens the service life due to grid corrosion on the positive plate. The corrosion is permanent. A voltage below the 2.40V/cell threshold strains the battery less but the capacity is low and sulfation sets in over time on the negative plate.
  Driven by diverse applications, two sealed lead-acid types have emerged. They are the sealed lead acid (SLA), and the valve regulated lead acid (VRLA). Technically, both batteries are the same. Engineers may argue that the word 'sealed lead acid' is a misnomer because no lead acid battery can be totally sealed.
  The SLA has a typical capacity range of 0.2Ah to 30Ah and powers personal UPS units, local emergency lighting and wheelchairs. The VRLA battery is used for large stationary applications for power backup. We are looking at methods to restore and prolong these two battery systems separately.

Valve regulated lead-acid (VRLA)

The charge voltage setting on VRLA battery is generally lower than SLA. Heat is a killer of VRLA. Many stationary batteries are kept in shelters with no air conditioning. Every 8°C (15°F) rise in temperature cuts the battery life in half. A VRLA battery, which would last for 10 years at 25°C (77°F), will only be good for 5 years if operated at 33°C (95°F). Once damaged by heat, no remedy exists to improve capacity.
  The cell voltages of a VRLA battery must be harmonized as close as possible. Applying an equalizing charge every 6 months brings all cells to similar voltage levels. This is done by increasing the cell voltage to 2.50V/cell for about 2 hours. During the service, the battery must be kept cool and careful observation is needed. Limit cell venting. Most VRLA vent at 0.3 Bar (5 psi). Not only does escaping hydrogen deplete the electrolyte, it is highly flammable.
  Water permeation, or loss of electrolyte, is a concern with sealed lead acid batteries. Adding water may help to restore capacity but a long-term fix is uncertain. The battery becomes unreliable and requires high maintenance.

VRLA Batteries

A gel battery is classified as a VRLA, valve regulated lead-acid battery, which is a category of low maintenance lead-acid battery. These types of batteries are pre-sealed; the owner does not need to maintain them by checking their water levels. A gel battery contains far less acid than a traditional battery. In fact, they are filled with a gel substance, referred to as a gel electrolyte, that replaces what some of us know as battery acid.

Gel Batteries

The gel electrolyte is sulfuric acid combined with silica. The gel is immobile, like gelatin. Traditional batteries, however, are liquid or wet-cell batteries. A gel battery is referred to as a sealed battery, but this isn't completely true. A truly sealed gel battery would create gas build up, and dangerous levels of pressure. Gel batteries regulate their gas build up through openings in the seal.

Advantages Of Gel Batteries

Gel batteries have a few strong advantages that keep them on the market. They don't typically leak, or produce spills or corrosion. Even if they are cut open, the gel does not flow out of the battery. The batteries are not known to evaporate, which is a constant issue with traditional wet batteries. They have a better resistance to extreme temperature changes, and are more vibration-resistant and shock-resistant than other types of batteries.