I have experience with AGM batteries.

They suck for trolling motors.

Why is that? Knowing what I know about AGMs, they seem like they would be a
natural fit for use as with trolling motor. But I don't know of anyone who
actually uses them for trolling motors. But then again, I don't personally
know anyone who uses trolling motors.

Not to doubt you, but I would think that AGM's high amp-hour capacity, high
number of charge/discharge cycles in their expected life span, negligible
self-discharge rate, incredible capacity for high current draw, and ability
to recharge quickly to a full charge would be just the characteristics one
would want in a trolling motor battery. In fact, I'm pretty sure of it.
Out of curiosity, which brand of AGM batteries have you used, and how did
they fail to meet your expectations or underperform their flooded-cell
counterparts?

I've used AGMs exclusively on the boat for the last six years, and I'm
hooked on them. The brand I use are installed as OEM batteries in the
following boats:

Activa
Alden Yachts
Alexander Marine
Asia Harbour
Blue Water Yachts
Bounty Motor Yachts
Bradley Boats
Budsin Woodcraft
Cabo Yachts
Cabo Rico Yachts
Camargue
Channel Coast Yachts
Charles Didham Yachts
Cheunh Kee (friendship)
Christensen Shipyard
Cruiseline
Custom Steel Boats, Inc.
Derecktor Shipyard
Destination yachts
Dettiling Yacht Co
Double Happiness
Dyna Craft
Eastport Electric Boat
Elco (Lung Lee)
Electric Launch Co
Grand Banks
Grand Harbour
Hampton
Her Shine
Hinckley Company
Hines-Farley Offshore
Horizon
Island Packet
Jenn Huei
Jettern
Johnson
Kady-Krogan Yachts
Kha Shing
Lazzara Yachts
Lien Hwa
Lyman Morse
Maine Cat
Manta Catamarans
Moorings Ltd
Morris Yacht Co
Nordhavn
North Coast Yacht
North Sea Yachts
Nova Marine
Ocean Alexander
Oxford Boat Yard
Pacific Seacraft Corp
Pacific Trawlers
Palmer Johnson
Performance Yachts
Pierce Yacht Co
President
Queen Long
Sabre Corporation
Sam L Morse Co.
San Juan
Shanghai Baodoa
Skipperliner Yachts
South Coast
Symbol
Ta Chaio Chou
TA Shing
TA Yang
Tania
Transworld
Tung Hwa
Vicem Yachts
Viking Yachts
Vision
Vitrech
Well Chance

I've got to admit that I don't see anything in this list that you would
typically associate with the use of a trolling motor, so there may very well
be something to your negative experience with them in that context.

RG