I think we need to distinguish between a regular wetcell battery and an 'agm' battery. The agm battery in my honda should have died a long time ago, but it's still good and still takes a charge. The wet-cell battery in my savage died last month, and I foolishly bought another wet-cell, without considering the difference.  wet-cell is old tech, agm's are newer, but not the latest tech.
correct me if I'm wrong.

A few years ago I decided to educate myself about batteries.  I read a lot and learned how to use a multimeter.  I found out that after 40 or 50 years of thinking I knew about batteries, I did not know a lot and most people don't know much about them either.  I have five bikes and with the help of a smartcharger and lots of riding I have been getting 5 to 9 years out of my batteries and have yet to be stranded.  The secret is to keep the battery fully charged.  If you are not riding a lot you should hook up a pigtail and use a smart charger between rides.  Batteries last a long time if you do with them as the instructions say but having a fully charged battery ALL of the time is the rule of thumb.

Beagle, if that is the battery, it is a "regular" one. I would put them on a trickle charger if not ridden for more than a week or 2. I think they should last a month (from what I've researched), but that would be for a new one. After 3 years, I am sure it has weakened. I have an AGM battery. Technically, it should last 6 months before needing charged as it is new-ish. I left it parked for the winter (about 2 1/2 months) and it turned over flawlessly in the spring and my scooter fired in just a couple of revolutions. I bought the most powerful one I could find that fit the bike. I think I paid $120 for it at the local Batteries Plus store. I won't buy anything else.

This is the replacement model for the AGM battery I originally purchased:

http://www.batteriesplus.com/product/40578-DURAGM--15L--US-Duracell-Ultra-AGM...

In the 30+ years of my motorcycle experience I've had mostly flooded type batteries. Some have had long lives and others not so much.
A motorcycle battery is at the bottom of the food chain. Built to be as light and as small as possible, I think it's a crap shoot beyond a couple of years. Having said that, there's no reason to go out and replace something that's working. A load test is the best indicator of a battery's health. Shops that sell batteries can do this or load testers are available for cheap $ these days. I've had batteries that gave me a green light on the tender but failed the load test.
Like others have said, keep it charged with 2 amp or less charger.