Sealed batteries are made with vents that (usually) cannot be removed. The so-called Maintenance Free batteries are also sealed, but are not usually leak proof. Sealed batteries are not totally sealed, as they must allow gas to vent during charging. If overcharged too many times, some of these batteries can lose enough water that they will die before their time. Most smaller deep cycle batteries (including AGM) use Lead-Calcium plates for increased life, while most industrial and forklift batteries use Lead-Antimony for greater plate strength to withstand shock and vibration.
Lead-Antimony (such as forklift and floor scrubber) batteries have a much higher self-discharge rate (2-10% per week) than Lead or Lead-Calcium (1-5% per month), but the Antimony improves the mechanical strength of the plates, which is an important factor in electric vehicles. They are generally used where they are under constant or very frequent charge/discharge cycles, such as fork lifts and floor sweepers. The Antimony increases plate life at the expense of higher self discharge. If left for long periods unused, these should be trickle charged to avoid damage from sulfation - but this applies to ANY battery.
As in all things, there are trade offs. The Lead-Antimony types have a very long lifespan, but higher self discharge rates.
Batteries come in all different sizes. Many have "group" sizes, which is based upon the physical size and terminal placement. It is NOT a measure of battery capacity. Typical BCI codes are group U1, 24, 27, and 31. Industrial batteries are usually designated by a part number such as "FS" for floor sweeper, or "GC" for golf cart. Many batteries follow no particular code, and are just manufacturers part numbers. Other standard size codes are 4D & 8D, large industrial batteries, commonly used in solar electric systems.
Some common battery size codes used are: (ratings are approximate)
|U1||34 to 40 Amp hours||12 volts|
|Group 24||70-85 Amp hours||12 volts|
|Group 27||85-105 Amp hours||12 volts|
|Group 31||95-125 Amp hours||12 volts|
|4-D||180-215 Amp hours||12 volts|
|8-D||225-255 Amp hours||12 volts|
|Golf Cart & T-105||180 to 225 Amp hours||6 volts|
|L-16, L16HC etc.||340 to 415 Amp hours||6 volts|
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