Flooded Lead Acid Batteries
Lead acid batteries are the most common deep cycle battery type. They have been in common use for a long time which means they're fairly well understood. They have seen minor efficiency improvements over the years, though efficiency in addition to capacity drop as they age.
Even so, of all the energy storage media available, lead acid batteries offer the most bang for the buck (watt-hour capacity per dollar spent) at least over the short term. As a result, they are extremely common. Much of the renewable energy equipment on the market is designed to work within their voltage range. And they're 100% recyclable.
Our lead acid batteries need regular use, maintenance, and ventilation to thrive, so are a much better choice for full-time off-grid homesteads than for occasional or emergency backup power.
Lead acid batteries must be protected from the elements. Direct sunlight would damage their housing, heat shortens their life, and low temperatures result in reduced effective capacity and freezing will damage their plates. For best results, keep your batteries cool and dry, check water level often and deal with any corrosion early and often.
Flooded Lead Acid Batteries from Real Goods