Standard Flooded Lead-acid Batteries

Flooded Lead Acid is the most cost effective deep cycle battery technology for solar electric power systems. Sure, it's comparatively low-tech, but flooded lead acid batteries are reliable, low cost and surprisingly efficient. Since weight generally isn't an issue in stationary applications, a quality flooded battery provides long cycle-life with a minimal initial investment compared to other technologies. True deep-cycle batteries can withstand discharge cycles as deep as 80% without damage. With initial charge/discharge efficiencies well over 90%, these batteries are a good choice.

Today's deep cycle flooded batteries benefit substantially from technological improvements, allowing premium battery manufacturers to offer 10-year warranties for their best products. Lead-acid batteries are fully recycleable, making them a "green" choice for energy storage. In fact, the majority of the lead in a new battery is actually recycled from old batteries.

In our experience, flooded deep cycle batteries can be loosely grouped into four categories of quality:

Marine batteries are a compromise between a starting battery and a true deep cycle battery. In fact, calling them deep cycle is a bit of a stretch, regardless of what it says on the side. These batteries are not really suitable for off-grid applications and will not last long under residential use. They are appropriate for boats and RVs if they are not discharged deeply and you don't mind replacing them every two years or so.

Golf cart batteries are a true deep cycle design, but they are the "economy" version. Golf cart batteries come in several sizes, but they are built to sell at a low initial price and deliver a correspondingly shorter lifespan compared to their bigger cousins. These batteries are considered by some to be a good "starter battery" for those who are new to off-grid systems because newbies often misunderstand or neglect their batteries. Batteries of this size are appropriate for smaller systems, but chaining together more than a dozen golf cart batteries is a poor idea. Much better to get a physically larger battery to match the system. Expect 3-5 years lifespan with proper care.

L16 batteries have become a standard for "mid-size" systems when low initial investment is a primary factor. Generally, this physically larger battery will deliver longer life than golf cart batteries, and performance is better too. Larger cells allow fewer batteries to be used, and that reduces the number of connections. Parallel connections within the battery set are reduced also. Although the initial investment cost of L16 batteries is lower than "premium" batteries, the cycle-life is also much less and so the long term cost usually exceeds the price of a premium-class battery. Expect 5-7 years lifespan with proper care. We've seen competitors claim 8-11 years lifespan for a L16 battery such as the Trojan L16-RE-B.  That's the sort of optimism that gets people playing the lottery every week. It may actually be possible if you treat your battery very well, use it gently and have very good luck.

Premium-class deep cycle batteries generally deliver the lowest operating cost over their lifetime, along with better performance. Best suited to mid-size and larger battery systems, these batteries are usually characterized by physically larger cells so it takes fewer of them to make a full battery set. This reduces the number of connections in the system and often eliminates the need for parallel connections. Premium batteries are built to a higher sytandard and with thicker internal plates, further contributing to their extended deep cycle performance and longer life.