How To Choose a Battery Charger

Choosing a Marine Battery Charger

When choosing a marine battery charger, it is important to choose one that charges your battery as accurately and efficiently as possible.

The Demands of a Marine Battery Charger
Choosing a battery charger for your boat can be more complicated than choosing other marine electronics because there are additional factors to consider when charging batteries in a marine environment. The following factors will affect what charger you should choose for your particular marine batteries and needs.

Charging takes place under a variety of environmental conditions.
Charging is done under electrical conditions with an imperfect sine wave.
There is always a risk of overcharging the battery with the wrong charger.
Configuration of the battery bank during charging.

All of the above factors should be carefully considered when choosing a marine battery charger for your needs.

Determine Your Battery Type
In order to select the right charger, you need to know the specifications of the battery that you want to charge. Determine your input voltage, battery type, and amp-hour capacity.

Input voltage for marine batteries is usually 120 or 230 VAC.
Battery type is typically either gel, flooded, or AGM.
Battery capacity is listed on the battery as "Ah".

Choose a Charger That Won't Overcharge
One of the fastest ways to degrade a battery is choosing a charger that either overcharges or undercharges the battery. Overcharging can overheat the battery, it can cause excessive water loss in flooded batteries, and in general you run the risk of damaging your batteries. The correct rate of charging is based on the battery capacity, which you determine from the "Ah" rating listed on the battery. A safe charging rate is accepted within the battery industry as about 20 percent of the Ah capacity of your battery. This means that a 100 Ah battery would ideally be charged at a 20 Adc rate.

Using a Battery Bank
It is common practice by many mariners to connect battery banks of various capacity batteries to the charger. While the ideal condition would be to run the same capacity batteries on the same bank, sometimes this isn't realistic. You can connect different capacity batteries to the same bank as long as you choose a battery charger that is sized based on the capacity of the smallest battery bank. This will protect the potential of overcharging and overheating any of the batteries with the smallest capacity. However, you may still experience longer charge times for the larger banks. If this becomes a problem, it would be a good idea to invest in a new charger that's more closely rated for the larger banks in your system.

Typical Charging Times
The table below displays the typical charging time for the three standard battery sizes.

Choosing a Marine Battery Charger: Time to Purchase
When you are ready to purchase a charger for your boat, whether it's a portable or an on-board one, don't just go out and buy the first one you find. Take the charger ratings that you've calculated above and comparison shop to find the best price.

The Benefits of Battery Chargers
A well rated battery charger will ensure that your batteries last longer, and that you get more use out of them. There is nothing quite as convenient as a quality on-board battery charger. It brings you peace of mind so that you can enjoy the activities that you are out on the water to enjoy, like sailing, fishing, water skiing, or exploring.

**Approximate Charging Time in Hours**
Battery Size	10A	20A	40A
30 Ahr	2 hours	Do not use	Do not use
75 Ahr	5 hours	Do not use	Do not use
100 Ahr	6.5 hours	3 hours	Do not use
200 Ahr	12.5 hours	6.5 hours	3.5 hours
230 Ahr	Do not use	7.5 hours	4 hours
460 Ahr	Do not use	15 hours	7.5 hours

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