AGM & AGM Battery

The AGM refers to Absorbent Glass Mat, it's kind of glass fiber material. AGM is one type of separators used for lead acid battery, the other types of battery separator could be plastic material, such as PE or PVC separator, and Phenolic Resin fibre. Lots of the lead acid batteries selling in the global market are using AGM separators, hence they are known as AGM batteries.

Electrolyte / Acid & Gel

There are two popular types of electrolyte using for lead acid batteries, Sulfuric Acid H₂SO₄ or Gelled=Sulfuric Acid H₂SO₄ mixed with Pyrogenic Silica SiO₂, the batteries with Gelled electrolyte is also known as GEL battery. The electrolyte could be formulated to different gravity density as per the acid contained. The higher density of acid would boost up the initial capacity of a battery but shorten its life time in return, because the higher density of acid would bring faster corruption to the battery plates especially the grid of the plate. But low density of acid might slow down the capacity boosting shown as lower capacity.

SLA Battery & SMF Battery

SLA Battery refers to Sealed Lead Acid Battery.

SMF Battery refers to Sealed Maintenance-Free Battery.

The separator of both SLA and SMF battery could either be AGM or Plastic.

The electrolyte of both SLA and SMF battery could either be Acid or Gel.

Sealed =  Maintenance-Free = Management-Free?

Probably it would be agreed on Sealed=Maintenance Free. The battery is sealed, you cannot open it manually or don't need to open it, hence it appears nothing needs for the batteries and just let them running in their way, maintenance is no needed.

Sealed and Maintenance-Free doesn't mean Management-Free, especially when the batteries are using in strings as battery banks typically in the sizable UPS systems. Most of the time one single battery failure or fallen behind would result to whole group battery failure and make power supply unstable. Hence the BMS (Battery Management System) would be greatly important to keep stable power backup service. The battery could be Maintenance-Free, but you need to Manage it.

Is AGM Battery Sealed and Maintenance-free?

Not all, but many. The AGM is just a kind of material of battery separators, hence the AGM separator cannot determine the battery is sealed or not, neither AGM has nothing to do with battery sealing. But since a lot of sellers are referring AGM battery as SLA battery or SMF battery, so the end-users were educated and accepted with AGM battty as Sealed and Maintenance-free.

Conventional, Traditional, Flooded, Wet batteries

Four different words might lead to the same type of lead acid batteries, the Un-Sealed battery which has been developed over last decades. It's an old technology of battery assembly when sealing process has not well been invented. These batteries are also kind of lead-acid battery, comparing to SMF Battery, the C/T/F/W batteries are Maintenance-required due to the open-able vents. The electrolyte would be evaporated during battery operation together with gas emission, hence it's important to carry on regular maintenance (to check and do complementary acid filling) and to do topping up charging.