The chargers for power-tool batteries (which I assume this is) have regulator circuitry which will almost certainly adjust for the slightly reduced input. Don;t forget that the 110 and 120V rating are only nominal voltages.
An American 120V supply can drop several volts under load, and a U.K. 110V site transformer can easily be a few volts over if not fully loaded.
Re: U.S. Battery charger U.K. 110 volt supply#142071 12/01/0407:51 PM12/01/0407:51 PM
The usual types of regulators can indeed only adjust downward from whatever voltage is fed into them, but the supplies are designed in such a way that the input voltage will still be sufficient even when the AC line drops to its lower limit.
Re: U.S. Battery charger U.K. 110 volt supply#142073 12/06/0401:00 PM12/06/0401:00 PM
You should probably be allright, as a bunch of these chargers use switching power supplies nowadays. They will adjust internally to accomidate for line voltage variations. Even if your charger is one of the lower tech xfrmr types it will most likely be no problem as 110V is well within tolerance here in the states. Ian