Some "battery tenders" will not charge a battery from dead, but only maintain from a normal operating state, or just a few volts below normal.
You will need to use something like a 10 amp charger to get it "up" and then use some type of battery tender to maintain between drives.
I keep my battery tender on my '76 Shovelhead as it's a lead acid battery and seems to drop a lot quicker than my '09 Roadglide AGM battery. Just a quick startup and idle every couple weeks seems to keep it going okay.
