Sealed Lead Acid batteries fall under the category of rechargeable batteries and if they are ignored, not charged after use, not charged properly or have reached the end of their intended life span, they are done.
If it’s completely dead, it’s gone and you need to find a replacement. If you are lucky and there is enough juice left, you can hook it up to a smart battery charger and get more life out of the battery while desulfating the lead plates and bringing it back around.
Complete the charge/ use cycle five times to see if this will remove the sulfur efficiently enough to restore performance to the battery. To do this, fully charge the battery, use the battery until it is depleted, then repeat this cycle five times.
Hopefully you get lucky and can get more use out of the battery if it’s not critically damaged.
On the negative side, the longer after initial use it sits without operating or the longer into its life span, the less of a charge it will hold if any. When the battery is new, it should be at 100% capacity, meaning it is holding the full charge it was intended to.
Batteries that sit for a length of time after use without a charge or that are near their intended lifespan will perform badly as well as lose the ability to hold a full charge. Instead of holding 100% capacity, it will gradually drop down to 90%, 70%, 40%, etc. until it is dead.
The best practice to extend the life of your battery is to give it attention, especially during those winter months. It can’t sit idle for a length of time and be expected to perform when needed.
I recommend using a smart charger (trickle charger) to allow the battery the chance to maintain itself and give you the most bang for your buck when not operating.