Basically the higher amps will allow you to charge a battery in a shorter period of time.
When a battery charger says it is charging at 2 amps or 10 amps it is describing the number of amps it is delivering to the battery per hour. So when you are charging a battery at 2 amps then it takes 24 hours for the battery to receive 48 amps of charge. The basic car battery is a 48 amp battery so it would take a 24 hour period of charging at 2 amps for the battery to receive a complete charge.
Is Faster Better?
The faster charge may be more convenient but faster charging is not always the best type of charging for deep cycle battery. The plates inside the battery can be buckled or disfigured when the battery is charged at faster speeds. A faster charge is rarely ever recommended for smaller batteries that power lawn equipment, motorcycles, and personal water craft. The faster charge can often damage these smaller batteries.
Most battery manufacturer’s, and expert mechanical technicians recommend a combination charge for batteries. The 10 amp charge is a great starting charge for when the battery is almost completely depleted of energy, but as the battery gains power then the charging amps should be switched to a 2 amp charge so the battery slowly finishes receiving the final amount of charge that it needs. By charging your battery in this manner you avoid damages that can occur to the battery plates.
A deep cycle battery does not actually charge any differently than a normal car battery does. A deep cycle battery has thicker plates inside them so they are not as easily damaged and they do not have sulfate corrosion happen as easily.
Deep Cycle Batteries are Better able to Handle Complete Depletion
When a battery is used until it is depleted the plates inside the battery corrode quicker because of the frequent depletion. Once a battery starts to corrode on the inside you are usually looking at a useless item that is good for nothing more than using it as an exchange core. A deep cycle battery is specifically designed to last longer before it is completely depleted and then to resist damage from frequent depletion.
Maintenance or Float Charges
One thing that most deep cycle batteries do require is a maintenance or float charge because boats and equipment that have deep cycle batteries are often stored for several months and their batteries lose power during storage.
You want a battery charger that provides a 2 amp float charge and not one that provides a 2 amp trickle charge. The 2 amp float charge will take the battery to its optimum charge and then the battery charger will stop charging until it senses that the battery has lost some power. A trickle charger will provide 2 amps of charge continuously even after the battery has a complete charge. This trickle charging can allow the battery to be over charged and that can cause the plates to buckle or other internal damages which will shorten the life expectancy and the performance abilities of your battery.
Are Automatic Chargers Better?
A battery charger for a deep cycle battery that has the ability to provide either 2 amps or 10 amps per hour will usually have an automatic setting. By choosing to use the automatic setting you can allow the technology built into the charging unit to determine how much of a charge your battery needs, and then the unit will switch from a 10 amp fast charge to a 2 amp slow charge when it is appropriate to do so. These automatic battery chargers increase the life expectancy of your batteries because they seldom do any damages to the internal battery components.
Does the Way a Battery is Used Determine How it should be Charged?
Some people will tell you that you should charge the battery that you use to crank your boat at 10 amps, because it has to discharge a lot of power when it cranks the boat, and then use a 2 amp charge on batteries that power accessories like the trolling motor because the trolling motor pulls very little power from the battery at one time. This is completely a myth.
It does not matter if the battery will provide a lot of power at one time or a slow continuous amount of power. The alternator on an engine provides a slow and continuous charge even though the battery puts out a high amount of power when the engine is first cranked.
Voltage is Important
Remember that you want your battery to receive the proper voltage and a steady charge until it reaches maximum capacity. Be sure that you either know what voltage your battery requires or that you are using a battery charger that will automatically determine the voltage requirements and make adjustments for the needs of the battery.