What is the difference between a sealed maintenance-free battery and a VRLA battery?
Not to be confused with maintenance-free car batteries, so-called ‘sealed maintenance-free batteries’ were introduced for stationary applications in the early 80s. While these batteries are ‘sealed’ to the extent that there is usually no access to the inside of the cell, many users misunderstood the term and installed these batteries in areas with no ventilation. Such batteries periodically release small amounts of hydrogen in normal service, and can produce large quantities of this flammable gas if overcharged. On the maintenance side, it has been found that these batteries can be unreliable if neglected. In addition, IEEE has published a recommended practice for maintaining and testing these batteries. With these facts in mind, the industry has moved away from the term, ‘sealed maintenance-free’ and has agreed on ‘valve-regulated lead-acid’ (VRLA).
