Comparing Marine Battery Technologies
(Gel, Absorbed Glass Mat (AGM), Flooded Lead Acid, and Nickel-Cadmium)
While I was on a month long assignment in Washington DC in 1999, I read an article on battery management in the 1999 Ocean Navigator "Annual" issue that I thought was deeply flawed. The contributor, Chuck Husick, illustrated how he thought one should maintain and configure a marine battery system. Some of his key recommendations ran counter to accepted industry policies and physical laws that I had read about in Nigel Calders excellent Boatowners Mechanical and Electrical Manual, as well as web-resources like the Ample Power web-site and their line of books.
The research I conducted for my letters to the editor led to this collection of web pages. For my purposes, Lifeline Absorbed Glass Mat (AGM) batteries are the best choice, but every battery technology has its strengths and weaknesses. Naturally, I have no commercial affiliation with any battery or charge system manufacturer. I suggest you start off with my Lead-Acid Battery Glossary Page to familiarize yourself with all the terms that will be used throughout this site.
Learn more about the different types of marine lead-acid batteries currently on the market with my page on lead-acid battery technology (Flooded, Gel, and AGM). I discuss the features of traditional flooded lead-acid batteries commonly found in cars and most boats versus Valve-Regulated Lead Acid (VRLA) batteries like Gel and AGM. Each battery technology has its virtues and its downsides, so it is important to understand them and then make the decision which best suits one's own needs.
Next, I researched what sensible people have written about how to size your battery capacity. The industry consensus is usually 4x your daily energy needs, although it depends on the type of battery your have on board, as well as your charging system, available space, weight considerations, and usage profile. However, starting off with at least 4x allows you some breathing room later when/if you add more electric circuits.
On another page, I have assembled a number of arguments why the average marine user would only want two battery banks on board (house + starter) and how such a bank configuration leads to better battery performance, longer battery life, and higher safety. Basically, the less you discharge a battery, the better. Fast discharges are also harmful and lower available battery capacity (see Peukerts law).
Chuck Husick made a number of assertions in his responses about battery costs, so I looked into those as well. A cost model later, I had a number of startling results. Namely, that AGMs worked out to be less-expensive for my marine application, despite having a high initial cost, due to their superior features. Over the life of the AGMs we would save a lot more on lower maintenance costs, fuel consumption, etc. than the premium we spent initially (when such a premium exists).
I then go on to explain how my bulk charging model works. This is a rather simple cost model (hey, it's my spare time) but it covers the battery conditions usually found on cruising sailboats ( bulk-charging, i.e. not fully charging the battery banks except on occasion). The model is available for free and runs on Microsoft Excel (see the page for details). A later cost model also looks at replenishing batteries beyond the bulk stage.
I then go to wrap up my marine battery technology findings in the Conclusions page. I detail what battery technology I chose and why.
For those who are interested in the written volleys between myself and Chuck Husick, I have preserved the e-mails for your review. I found the exchange quite amusing and thought-provoking. While his essay made me research this topic enough to make an informed purchase decision, Chuck Husick has yet to convince me and the rest of the battery industry that his ideas are superior. After all, when confronted with contradicting evidence, he decided to "withdraw from the discourse".
Anyway, last but not least, I have assembled some