How do you charge RCL 3000 lamp?

According to one of the Battery Companies, you mathematically take the battery rating and divide by the charger rating. The 6v/4aH battery (6V at 4 ampere Hours) has a rating of 4 ampere hours and the charger that comes with it has a rating of about 1/3 amps output. Therefore, you would need 4 divided by 1/3 or 12 hours to charge it. Having said that, the owners manual that comes with the lantern states to charge it for 18 hours. The extra time might be that the output of the charger slows as the difference becomes less when the battery develops a charge that makes the charging more difficult to push current into the battery.