I think what is going on here is the confusing of a "GEL" battery with an "AGM" battery.
They are two different animals. They are both sealed Maintenance Free batteries but are of different internal designs. I don't have the exact difference in hand, perhaps someone knows how they actually differ?
About all I recall is the "AGM" and "GEL"design have similar advantages over the old wet cell batteries we all know and love, (not).
Each has its own good points and bad points, but in our world it appears the only battery widely available for the GL1800 are of the "AGM" type.
Dry cell batteries are new to me so I have no idea how they compare to AGM and GEL??
Arn't dry cell batteries used a lot in race cars due to their reduced weight??
The Westco battery being advertised by Wingstuff as a "GEL" battery is incorrect, it is an "AGM" battery. The same class (AGM) of battery that came in your GL1800 when new, The Yuasa YTX20L-BS, YTX20HL-BS, (Which appears to be the "Best Buy" for a GL1800).