A VRLA battery (valve-regulated lead-acid battery), more commonly known as a sealed lead-acid (SLA) or maintenance free battery, is a type of lead-acid rechargeable battery. Due to their construction, the Gel and AGM types of VRLA can be mounted in any orientation, and do not require constant maintenance.The term “maintenance free” is a misnomer as VRLA batteries still require cleaning and regular functional testing. They are widely used in large portable electrical devices, off-grid power systems and similar roles, where large amounts of storage are needed at a lower cost than other low-maintenance technologies like lithium-ion.
There are three primary types of VRLA batteries, Sealed VR wet cell, AGM and Gel. Gel cells add silica dust to the electrolyte, forming a thick putty-like gel. These are sometimes referred to as “silicone batteries”. AGM (absorbed glass mat) batteries feature fiberglass mesh between the battery plates which serves to contain the electrolyte. Both designs offer advantages and disadvantages compared to conventional batteries and sealed VR wet cells, as well as each other.