BU-201b: Gel Lead Acid Battery

Learn the unique advantages of lead acid batteries

The early gelled lead acid battery developed in the 1970s converts liquid electrolyte into a semi-stiff paste by mixing the sulfuric acid with a silica-gelling agent. AGM arrived later and both gel and AGM batteries offer slight differences in performance. Cashing in on these unique characteristics; the gel batteries are commonly used in UPS, big and small, while AGM has carved out a market with starter and deep-cycle applications. Gel and AGM batteries are part of the vale-regulated lead acid (VRLA) family.

Energy storage systems (ESS) deployed for frequency regulation and energy buffering use lithium-ion batteries. Unlike lead acid, Li-ion can be rapid charged on excess energy and can switch to discharge in milliseconds. While UPS normally dwells at full-charge and is only discharged occasionally, Li-ion in an ESS can operate at mid-state-of-charge of 40 to 60 percent without inducing sulfation.

A gel battery generally lasts longer than AGM, and improved heat transfer to the outside is one reason. (The gel separator moves heat whereas the absorbent glass mat of the AGM acts as insulator.) A further advantage of gel is the dome shaped performance curve that allows the battery to stay in the high performance range during most of its service life before dropping rapidly towards the end of life. AGM, in comparison, fades gradually. Gel is known for good performance at high ambient temperatures, is less prone to sulfation than other systems, but it needs the correct charge and float voltages.

In terms of suitability and cost, the flooded lead acid is most durable when used in standby operation, but it is also the most expensive and requires maintenance by replenishing water. Gel is cheaper than flooded and is the preferred battery for the UPS installations in communications. AGM comes at a lower cost and is also superior in load capabilities to gel. Table 1 illustrates the advantages and disadvantages of the gel battery over other lead acid systems.

Advantages Maintenance free; can be mounted sideways
  Long lasting due to its ability to transfer heat to the outside
  Performance stays high until the end of life, then drops rapidly
  Produces water by combining oxygen and hydrogen
  Safe operation and forgiving if abused
  Large variety of battery sizes available
Limitations Higher manufacturing cost than AGM but cheaper than flooded
  Sensitive to overcharging (gel has tighter tolerances than AGM)
  Moderate specific energy and load current
  Subject to release gases. Ventilation needed
  Must be stored in charged condition (less critical than flooded)

Table 1: Advantages and limitations of the gel battery.

Last updated 2017-05-31

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