I have a cheap 1 amp charger that gets hooked up every 2 months for 6 hours. I had a smart charger and gave to my son. Many don't understand how these work, one thing I can caution on, do not leave connected to the battery without having your 120VAC connected. Most of these smart chargers go through a cycle similar to a deep cycle marine battery, part of the cycle it uses a LED to discharge the battery, this is to prevent sulfation https://www.crownbattery.com/news/su...ry-maintenance
. Since I have a long history of batteries, made my own smart chargers over 30 years ago, many may be puzzled why I of all people would have a cheap charger, I included the link, note what they say about storing in a warm environment, my garage never goes below freezing, average winter temp. is around 40 to 50'F , yes I was brought up using F but we converted, so some is 'C some 'F same with measurement , I use feet not centimeters . OK back to topic,my battery is fully charged and like I said I charge it about every 2 months for 6 hours at a maximum of 1 amp, my batteries last about 5 to 6 years, keep in mind I have a series regulator which can drastically reduce the life of the AGM battery.
I mentioned making smart chargers over 30 years ago, I dealt with nickel cadmium, NI-MH nickel metal hydride batteries and also the newest lithium multi cell , I was also involved with lift truck batteries . The key is having a charger that is designed for motorcycle batteries and following proper procedure. I did a post on AGM batteries and tied that with the shunt and series regulator. Looking at the cost of a battery , is roughly the cost of a series regulator.
As to starting the bike, I use stabilizer, I have had cases where I already had it in the fuel and the weather warmed up then went for a ride, so by late November I will be running stabilizer . Others have said it, unless you plan on riding for a minimum 15 minutes after reaching full temperature, not a good idea, as condensation will occur.