If you run a charter service or other boating business, batteries are usually the only source of electricity available once you leave the dock. In general terms, batteries used to start the boat are "regular" batteries; the same ones used to start cars every day. It's the deep cycle marine batteries that you can discharge deeply and recharge without ill effects, which power lights and on-board electronics, that require thoughtful consideration prior to purchase.

Deep cycle batteries are all lead-based, but there are 3 main types of lead-acid batteries: flooded acid, gel cells and Absorbed Glass Mat (AGM). The most common type, flooded acid batteries, aren't sealed so care must be taken that the liquid electrolyte inside doesn't spill out; they also require maintenance to replenish the electrolyte inside from time to time. Flooded acid batteries come in the most sizes and are typically the cheapest option. Gel cells, the next step up, contain a thickening agent so that the electrolyte solution can't slosh around. The gel also prevents leakage should the battery case crack. Absorbed Glass Mat (AGM) batteries are the most recent advance in marine batteries. They're the most expensive, but they're the most impact and vibration resistant and offer other advantages including fast charge dispensation. Here are a few things to consider:

1. Analyze your boat battery applications and capacity needs.

2. Gather information on marine batteries and consider marine lead acid batteries and gel boat batteries, based on your specific application.

3. Comparison shop for the best deal.

Action Steps
The best contacts and resources to help you get it done

Analyze your daily usage, determine size and capacity

The rule of thumb for deep cycle marine batteries is to have about 4 times your daily energy requirement. Other variables, such as your battery technology, charging system, available space and usage may argue for either a weaker or more robust marine battery system. Get boat batteries appropriate for your application: to start engines or to power equipment for hours.

I recommend: Websites like Lifeline Batteries and Apex Battery include charts and information helpful in choosing batteries.

Compare marine lead acid batteries vs. gel boat batteries, based on your specific needs

Determine which technology--flooded acid, gelled acid or Absorbed Glass Mat (AGM)--is best for your budget and usage profile. If the batteries are going into the bilge, you'll want gel or AGM batteries: both can operate under water, oriented in any direction. It's also important to research the advantages and disadvantages of hooking up batteries in series or in parallel.

I recommend: West Marine and 1st Optima Battery Sales evaluate the features of flooded acid, gelled acid and AGM batteries.

Research the best deal on marine batteries online

Now it's time to buy a boat battery. Obviously, batteries are heavy, so shipping 100 lbs. of batteries halfway across the country may not be cheaper than buying locally. It's still a good place to find marine batteries for sale, however, as it allows you to comparison shop websites offering wholesale marine batteries and local merchants in your area. Compare statistics such as reserve minutes, battery capacity and longevity.

I recommend: The are dozens of websites that offer wholesale marine batteries for sale. Useful sites include eBatteriesToGo and Exide Technologies.

Tips & Tactics

Helpful advice for making the most of this Guide

• •  Ask around your local marina for tips and advice; most sailors are glad to share their experience and advice.