Battery Info SLA 2

Smaller systems like those that use one or two AA batteries usually are better suited to different battery types with higher energy densities like "alkaline" batteries or "nickel metal hydride" batteries. Those types are more expensive, but they pack more energy into a smaller, lighter package so they make more sense for running things like small flashlights or cameras. Larger battery operated systems like those used to store energy from a big wind turbine or solar panel to run the electrical system of a whole house, or the battery systems of boats or RV's are usually made with lead acid batteries, but often not the permanently sealed type.

The lead acid batteries used on large systems are often called "deep cycle" batteries, and have access ports for the user to perform basic checks and maintenance like adding more liquid from time to time. This type of large lead acid battery, though very powerful, would not be ideal for use on an electric bike or kit since the liquid could possibly spill and the weight of these systems is often in excess of 100 lbs.
Though  lead acid battery technology is one of the oldest around, this is not a bad thing. The technology has been proven and tested over many decades and production methods have been specialized to produce high quality, low cost types of lead acid batteries for thousands of different niche applications. Other battery types may be more 'high performance' in terms of weight or energy density, but lead acid batteries are a time-tested, proven, and reliable option for applications like electric cars and electric bikes.