As for AGM batteries, Odyssey
makes a very high quality battery. Their product line covers power sports through industrial applications. Not cheap, however. One gets what they pay for usually.
They don't have a battery for the XT225. Not sure about the XT250 or other motorcycles. They have a Battery Finder
page which allows you to put in your vehicle/motorcycle type and it will return their battery model.
I purchased an Odyssey battery for my Ford van. Amazon prime had it listed for $299.00 The Odyssey online store had it for $267.00 Orders over $50 get free shipping. The battery was here (via UPS) in about 3-4 days, well packaged and quality all the way. Fully charged too.
I'm a bit tired of replacing the automart limited life flooded lead acid batteries. I think over the life of a vehicle, these "cheaper" batteries are actually more expensive. Changing them out isn't a job I enjoy either. And they can go dead without warning.
For terminal grease I use NCP-2
which has always worked well for me. It wicks its way all over the contact surfaces and provides excellent protection against corrosion.