Assuming its a lead acid battery, (what comes in the bike), you did everything correctly by removing it before you left it. Batteries will gradually lose a bit even with nothing connected to them but usually there's enough even after 4-5 weeks to start the bike. Depending on the age of the battery and what kind of added load you normally have on the battery during normal operation, it may still be ok. If you have access to a battery charger, I'd charge it up with that rather than trying to have the bikes charging system do it. The bikes system will get it there eventually if you run it at high enough RPMs long enough but it really doesn't put out enough to recharge a dead battery if you aren't doing a lot of highway speed riding for several hours. I would not expect that you did damage to the battery, they gradually lose flakes of lead off the plates over time as they charge and discharge. As they lose the lead, they lose capacity to take a charge and wear out. If the levels of lead build up enough, the plates can short between themselves and turn two plates into one, effectively dropping the voltage down from around 12 to ten or even less if more that two plates short out. That's one of the reasons why a battery can go from what seems fine to completely useless randomly. That's a big reason why you might want to replace the battery if it's 3-4 years old but still seems fine. That's why I said at the beginning that depending on its age, it might be fine or it may not be fine...