Boat batteries have a pretty tough challenge. Usually, they are placed down in the engine room where it is humid and very hot. The heat and humidity makes the battery discharge faster. Sometimes the batteries are just lying around for weeks before they are discharged. Having the right battery chargers, therefore, is as much important as loading the right batteries in your boat.
Indeed, it is useless to spend much on batteries and skimp on your boat battery charger. Eventually, cheap or low-quality chargers could do more harm for you than good.
Go for good quality chargers.
Take note that a new, good quality 12-volt battery will typically generate between 13.0 and 14.5 volts as new batteries generate slightly more than 2 volts per cell. But as the batteries get older, they will produce less and less voltage and power per cell.
If you use a cheap battery charger, it will not be able to adjust for these changes in total voltage. This causes overcharging, which damages the battery and makes it lose its power rapidly.
On the other hand, choosing better quality battery chargers for your boat will be a wiser investment. These kinds of chargers may be much more expensive but they will save your batteries from overcharging. Factory equipped with devices, these chargers detect when the battery has reached its maximum charge level and then shuts down. Two manufacturers of good quality chargers for boat batteries are NewMar and Professional Mariner.
Right charging
In smaller boats, a silicone-controlled rectifier (SCR) battery charger may be the ideal choice. SCR charger varies its charge to keep your battery at a constant 13.4 volts. In live-aboards and larger boats, usually there are many 12-volt accessories that have ferro-resonant chargers that put out 12 volts continuously to keep up with constant power demands.
To maximize the full capacity of your boat battery, experts recommend that you follow the three-stage charging process. The BoatTech section of BoatUS (http://www.boatus.com/boattech/battchg.htm) tells us that the multi-stage charging works this way:
1. Bulk Stage: This first stage provides a constant amperage bulk charge of 25-40% of the battery's capacity up to about 14.4 volts (14.2 for gel cells).
About 75% of the battery's total capacity is restored during the bulk charge.
2. Absorption Stage: The remaining 25% of capacity is restored at a decreasing rate. Maintaining the battery at 14.4 volts (14.2 for gel), the amperage is steadily reduced. The battery is considered fully charged when it will accept only 2-4% of its amp-hour capacity at 14.4 volts.
3. Float Phase: The charge amperage has declined to 2-4% of the battery's capacity, and voltage drops to 13.5 (13.8 for gel cells). This maintains the battery without losing electrolyte from gassing.
4. Equalization: Applies to lead-acid batteries only. This fourth, manually triggered stage prevents lead-acid batteries from aging prematurely by applying a small, constant current until the battery reaches 16 volts, which dissolves the hardened lead sulfate crystals on the battery plates and prolongs battery life.
You can prolong the life of your battery life by charging your batteries to its full capacity. Many boaters tend to reduce charging time to save on engine power but this could eventually prove detrimental to your battery.
So to avoid hassles with your battery, remember to have good quality battery charger and to charge to the full.
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