These days, when a battery is dead, it's dead. Back in the day, motorcycle batteries and most car batteries had fill ports, so if the battery had lost its charge, you could open the fill ports, add a little distilled water and electrolytes, put the battery on a charger, and save it from death, thus avoiding having to buy a new battery. However, almost every battery these days is sealed, with no way of bringing it back from the dead. The only thing to do is replace it. And when replacing your battery, you should also always check the battery cables at both ends, since they can come lose, or worse, break.
We talked to Drag Specialties and asked the experts there about batteries. The first thing that came up was what size is needed for your bike-how big is your battery box and motor? Then they wanted to point out that not all batteries of the same size have the same cranking power. If you have a big-inch motor, you will need a battery to handle the size of the motor. Also keep in mind that you get what you pay for; a less expensive battery may not do the job on a big-inch bike, and most likely won't last long on a stock bike (for the most part). In this article we're concentrating more on what you should check and do, rather than which actual battery to purchase, so check out the Drag Specialties website to get the right battery for your bike.
We have a 95-inch Softail that sat in a garage over the winter and hadn't been started and run for quite some time, so when we did try to start the bike, the battery was dead. We put it on the charger, but after one day (a full 24 hours), the battery was still dead. It was a sealed battery, so the best thing to do was replace it.