tony.latham wrote:With most SLA's you can pop the cover and get at the cells to maintain them.
I didn't think you could actually open up an AGM? I've owned one for six months is all.
Tony
You are right about AGM. We should not try to open them.
Regular lead-acid batteries have easily removed caps or a gang of caps that are meant to be removed to be able to add water. They also spill quickly if tipped over.
A sealed lead-acid battery is sealed. No caps to remove. That are also known as VRLA batteries (valve regulated lead acid). The valve is a vent valve that releases pressure if necessary. They are sealed and therefore unspillable.
A maintenace free battery has a sorta hidden strip of caps that can be removed, but are usually not removed. These batteries could have water added or the sp. gr. taken to determine charge. They are the common type of starting battery that are used in cars. Not really sealed tight. If tipped they can leak electrolyte.
AGM are also VRLA and can be mounted upside down if wanted as their electrolyte is absorbed in special sponge-like glass matting between the plates.