try to hold a primitive tharger on for some 15 minuts..then svap back to the elektronic controlled type..often total flat batteries can not start loading ,,,and elektronic loaders can not start load if there not is some bit of poweer to give a indikation of the pos and neg terminals..and the load kondision of the battery.or use some start vires to trix the loader to beleve that there is a funktion battery..and after it starts loading just pull the ekstra battery.(.be care of sparks)