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[twalker H260]

If it is a group 54 battery it may or may not have an issue. Cca for a group 54 looks to vary from 220 to 350 or so cca. The CCA for your battery should be shown on a label on the battery itself. It may be appropriately sized to start the generator but may be undersized for use with the bow thruster if it is any distance from the battery. For determining what is an appropriate size we would likely need to know what model generator and what model thruster you have.

 

[Ralph Johnstone]

Hence the thinking that the AGM isn’t delivering adequate amps.

Which may be the result of the terminals on the AGM being dirty, which would produce a high resistance, which would reduce the amperage.

How are you determining 200A.? That tester only does 100A?

The single most important thing you can do here would be to listen to and follow Maine Sail's advice.

 

[SycloneDriver]

He is using a 100 amp load tester that is giving a test result of 200 CCA. Not 200 amps at 12.7 volts. This is an easy mistake if your not familiar with all the units and terms. It was probably about 100 amps @ 9.9 volts. Bad battery or bad connection.