Batteries are the heart and soul of most sailboats. Although there are still purists, most sailors have electrical systems on board that are supported through battery systems.
TYPES
Batteries for marine use fall into three basic categories:
Deep-cycle batteries are capable of supplying heavy loads on a regular basis.
- True deep-cycle batteries have thick lead plates that can accept and deliver large amounts of current for long periods of time.
- This construction allows them to accept, deliver, and store large amounts of current without harm and to be discharged to lower levels before needing to be recharged.
Hybrid deep-cycle models are a compromise between the ability to deep-cycle repeatedly and the ability to start engines.
- Plate number and thickness of hybrid deep-cycle models allow them to accept, deliver, and store reasonable amounts of current, yet still have the ability to start engines.
Starting batteries temporarily deliver the high current necessary for engine cranking.
- Starting batteries have thinner lead plates, and many more of them, than deep-cycle models.
- Having a large plate surface area allows starting batteries to deliver a high level of current to an engine starting motor, but only for a short period of time.
- Sustained high levels of charging or discharging current can damage the plates of starting batteries.
- Starting batteries are rated by the cold cranking amps they can deliver.
RATINGS
Marine batteries have individual cells wired in series. Each cell produces approximately 2 volts. A 6-volt battery has three cells and a 12-volt battery has six cells.
- Batteries are rated according to the amp-hours (AH) of electrical energy they can provide.
- The rating is typically given for different lengths of time it takes for the battery to go from full charge to complete discharge at different load levels. The faster the rate of discharge, the less total energy is available.
- Compare batteries for house loads using the manufacturer amp-hour rating at a 20-hour discharge rate.
ELECTROLYTE FORMS
The lead plates in a battery are suspended in an acid electrolyte that provides the necessary electro-chemical reaction. The electrolyte can be in one of three forms: liquid (wet), gels, or absorbed in a glass mat (AGM). All three types will perform well within a manufacturer’s given performance ratings and have lead-acid construction. The type of electrolyte is mostly a personal choice.
- Wet batteries
are more tolerant of charging voltage levels and can be periodically equalized to maintain uniform performance of the individual cells. - Gel batteries
can be mounted in a variety of positions and in general use do not "gas" or have electrolyte that can spill or cause harm to skin or clothing. They typically accept and deliver higher levels of current for their rating and have lower "self-discharge" losses when not in use. - AGM batteries
have some advantages of both wet and gel batteries. They are low maintenance and offer good levels of performance.
TIPS
- Choose true deep-cycle batteries for your house bank when system loads are heavy or when a dedicated engine starting battery is used.
- Choose hybrid deep-cycle models when one or two battery banks must supply house loads and be available for engine starting.
- Choose a starting battery that can provide enough starting power for your engine size and type. As a rule of thumb, diesel engines require more cold cranking amps.
- For best performance and long battery life make sure your batteries are adequately sized for your loads.
- Don't routinely discharge house batteries below 50 percent capacity and use dedicated starting batteries when possible.
- When choosing batteries, select the highest quality model that your situation calls for and your budget allows.
INSTALLATION
Fundamentals of DC electrical systems and a complete electrical toolbox are required for battery installations.
Toolbox
For the battery box:
- Screwdriver
- Drill and bits
- Bolts, nuts, and washers
For the batteries:
- Soldering iron or compact butane torch if required for connectors
- Multi-meter
- Wire ties and clips
- Tin-plated wire
- Heavy-duty terminal connectors
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