jrhendo I don't think it's too critical. I'd disconnect the positive lead from the battery, hook up the charger, turn it on. Look at the meter needle: if it slams to over 4A, turn it off and take the battery to a battery shop /auto electrician to charge. They've got special chargers. If it's under 4A leave it at least overnight, preferably 24 hours. It should be fine by then.
4 amps is very minimal at best so don't he alarmed its a lead acid battery your not going to do it any harm. HI is fine and i read the manual Hi is 4.5 amps low is 1amp lets call it a 10 amp charger at MAX out put I doubt it is tho.
Charge on hi till the needle on the amp meter comes down to 1 or 2 amps or lower then turn to low and let it do it thing for a few more hours.
"Hi-Boost Charge Rate: To revitalise a flat battery quickly, set the charge rate to Hi. Once the ammeter reads 2.5 AMPS and providing the battery is in reasonable condition there should be sufficient charge to start the vehicle. Maximum charging time - 24 hours."
Think like this lets say if the 240 has an 80amp alternator and was trying to change that battery up i would bet there would be at least 60amps going into the battery.
You don't need to take it to an auto electrician you will be fine bus as for RACT batterys I would replace it with a better one if you intend on keeping the car if there like our RAC batteries here in WA they are rubbish I have replaced so many failed ones that were under a year old in customers cars there just not good quality.