Which battery type is often referred to as maintenance-free?

The term "maintenance-free" typically describes battery types that do not require regular water additions or electrolyte level checks to maintain their performance. The sealed valve regulated flooded lead acid battery, often referred to simply as a sealed lead acid (SLA) battery, is designed with a built-in mechanism that allows for the recombination of gases generated during charging. This design minimizes water loss, thus eliminating the need for periodic maintenance.

Unlike traditional flooded lead-acid batteries, which require regular monitoring and topping off, the sealed valve regulated batteries are constructed to be leak-proof and can be used in various applications without the risk associated with handling corrosive electrolyte. This makes them particularly popular in photovoltaic systems where ease of maintenance is crucial.

Other battery types listed either require maintenance (like flooded lead-acid batteries, which need water replenishment) or do not commonly carry the same "maintenance-free" label. Gel batteries, while low-maintenance, typically still require some care in terms of charging practices. Nickel-metal hydride (NiMH) batteries also do not typically fall under the "maintenance-free" category as they can require specific handling to optimize lifespan.