Trickle charge is usually referred to as keeping a battery on the charger at a very low charge current. This is meant to keep the battery as full as possible over an extended period of time. NiMH chargers don`t usually include this feature. Some chargers like the Panasonic BQ-CC16 and BQ-CC55 use a 1-hour trickle charge to top off the battery. It might even be the wrong terminology as it is a fairly high Trickle charge and sometimes people call it a top-off charge. The BQ-CC17 on the other hand does not use this topping off. Likely because it uses a lower current, to begin with.