Gel cell batteries are constructed with a typical sealed lead acid design and are sometimes confused with absorbed glass mat batteries by outward appearance. Unlike AGM batteries, gel cells have a lower power output for their size, but do well with applications requiring a slower rate of discharge or where operating temperatures may be slightly...
M/F Check the label. If the battery possesses a label, its specifications will be written there clearly. Unfortunately, sometimes labels are lost or damaged and cannot be read.
M/F Look at the construction. Gel cell batteries have a sealed construction and appear as a plastic box with two terminals in the top. While this type of construction does not guarantee that the battery is gel cell, it does narrow it down for you.
M/F Check for corrosion around the terminals. Gel cell battery terminals will appear cleaner, as the silica that holds in the electrolyte does not allow for the escape of gasses that corrode other sealed lead acid battery terminals.
M/F Look for valves. There are many gel cell batteries made with one-way valves instead of vents, also to reduce gassing and terminal corrosion.
M/F Shake the battery gently. If no sloshing is heard, it is likely either a gel cell battery or an absorbed glass mat battery. Again, this narrows your search in identifying your battery.