Three years is about par for battery life in my experience also. If you visually inspect the battery electrolyte, you may notice a heavy accumulation of lead sulphate (white goop) in the bottom of the battery casing. Once the sulphate crystals buildup reaches the plates, the battery shorts out internally and prevents it from taking a full charge.
I have read and believe it true that; the older a battery is the longer it requires to charge and the correct charging rate also needs to be reduced proportionately. We are not talking small changes here either! When new, a battery will completely charge in less than 1 hour and when they are old they require many days to fully charge at a considerably reduced charging rate. Fast charging is also known to shorten a batteries life or even destroy the battery.
An really old guy told me to never sit a battery on the concrete floor either, always sit it up on a board or bench. The notion being that electricity is synonymous with magnetism and it’s trying to find its way to earth, sitting it on the ground will cause it to drain faster. Believe this part or not, totally your choice. But I sit mine up off the ground now because it’s not that hard to do and he might be right.