Battambang is 293 kilometres northwest of Phnom Penh by road. Buses run frequently and take about 4 to 5 hours depending on traffic; share taxis are faster (about 3 hours) but cramped. The road is good and passes through pleasant countryside. From Siem Reap, the road journey takes about 3 hours.
The boat from Siem Reap to Battambang is one of the classic journeys in Southeast Asia: a daylong trip by slow boat through the flooded forests and floating villages of the Tonle Sap lake and the Sangkae River. It runs in the wet season (roughly June to December) when water levels are high enough. The journey takes anywhere from 5 to 8 hours depending on season and boat. Book through guesthouses in Siem Reap.
Battambang does not have an active commercial airport, though a small airstrip exists. All practical arrivals are by road or boat.