I did a bit of looking up a few years ago on battery chargers, one rule of thumb is that your charger must be able to supply 10% of the amphourage in current, so a 100amphour battery needs a 10 amp battery charger, if your charger is a microcontroller type, you can slightly lower that apparently and get away with it, otherwise you end up not been able to fully charge the battery.
Its why I got the charger I did, it can pump out 10.5 amps and monitors the battery so it doesnt overcharge.
The below is some great info on batteries and chargeing I found elsewhere.
LEISURE/DEEP-CYCLE BATTERIES
A word of advice!
Take care to calculate all your 12 volt items and their requirements before the initial purchase as a lightly used battery will eventually be the most economic.
Leisure batteries are designed to give a steady low amp discharge rather than meet the sudden demand required from a car battery to start an engine.
The life of a leisure battery is largely determined by the depth of the discharge cycle. We will say as an example that a leisure battery that is discharged each time by 15% of it's capacity may last for ten years. The same battery discharged by 30% of it's capacity will last for 8 years, 50% for 5 years, 75% for 3 years and possibly being discharged by 100% lasting only 1 year.
A 100 amp hour battery delivers 100 amps for 1 hour. Or 10 amps for 10 hours etc in theory, but in reality you should never drain the battery that much.
Power is amp x volts, so 100amps at 12v = 1200 watts, or 1,2kW 1.2kW for 1 hour is 1.2kWh.
Any form of heating element will cause a rapid drain on a battery, an electric kettle for example, also remember that a non compressor type refridgerator relies on a heating element to function.
All batteries self discharge when not in use and leisure batteries will self discharge 7 to 10% monthly.
How to kill your battery dead!
1/. Uncontrolled Charging causes overheating and gassing.
2/. Used too little (memory effects, so cycle every 2 months)
3/. Stored discharged (sulphating, any flat battery left flat will be scrap within 3 months)
4/. Do not store on a cold surface as this rapidly increases the self discharge rate.
5/. Too much deep cycling (a good rule of thumb is not to go beyond 50% of the battery's endurance at worst)
Volts - State of charge
12.7V or over – 100%
12.5V – 75%
12.4V – 50%
12.2V – 25%
12V or under – Discharged
When battery manufacturers state that a battery has a capacity of 110 Ah they presume the battery will be operating where the ambient temperature is 25 degrees centigrade. For every 1 degree centigrade drop in temperature the battery capacity falls by 1%
The time required to recharge a leisure battery can be calculated as follows. The recharge time in hours equals the battery capacity in Ah, multiplied by the Depth of Discharge in %, multiplied by 0.8, multiplied by 1.5, divided by 100 times the charger current rating in Amps, plus one hour. For example, a 110 Ah battery, discharged to 50%, on a 10 Amp charger, would take about 7.6 Hours
