I have only been here a few months. So far the battery has only required water added, about every 6 weeks. Am kind of concerned about reports of it dieing in 3 or 4 years. So far other than me testing it the backup pump has never been used.
If I remember the documentation you can use other type deep cycle batteries but the low water sensor won't work.
Q. Do you need a Basement Watchdog battery? A. You can use any deep cycle marine battery, as long as it is not maintenance-free. However, there are several advantages to using a Basement Watchdog battery. The Watchdog battery accommodates the system a fluid sensor which will sound an alarm when the battery needs water a very important feature, since a dry battery will not perform. In addition, Basement Watchdog batteries run longer per charge, and last years longer. A typical marine battery will last 2-4 years, while the Watchdog battery will last approximately 5-7 years. Basement Watchdog batteries are shipped dry (without acid) so they stay fresh on the shelf indefinitely, while wet batteries have a short shelf life.
Seen lots of complaints about them failing in 3-4 years. So based on that they are no better.