A whole web site could be devoted to this subject but there are a few simple rules that provide a little information into a charge cycle for a deep cycle battery.
10% of C10
The 10% rule relates to the capacity of the battery at the 10 hour discharge rate as supplied by the manufacturer.
10% of the C10 capacity is the recommended maximum rate of charge and the recommended rate of discharge. Look at a typical deep cycle battery like say a T105. this battery has a typical C10 capacity of around 220 amp/hours.
10% of 220 = 22. This is the recommended charge rate in amps and the recommended discharge rate in amps that will ensure a long battery life.
A charger larger than this may be beneficial so that some load can be taken from the battery while charging is happening.
The pitfalls with battery chargers is that they are expensive and tend to be unreliable. They also tend to put less into a battery than the specification would suggest.
The reasons for this are many, but the most common is that battery chargers are often connected to poor quality generators that have a poor electrical waveform.