Fenceman cp900 battery and mains energiser the fenceman cp900 battery and mains energiser has a high power output making it ideal for all types of fences up to a maximum of 8km5 miles the cp900 is powered by a 12v wet cell battery not supplied or 4 x internal d cell batteries supplied which can be used for back up power when the 12v battery is charging constant power output throughout the useful life of the battery means that there is no loss of output as the battery voltage drops