Charging interval authorizations according to the techniques disclosed herein provide for credit reservation and charging of whole charging intervals across two or more credit containers (36) in or linked to a subscriber account (34), without the need for redefining the charging interval size, even where the types of credit units differ between or among the credit containers (36) used to authorize the charging interval. Among the various advantages, the disclosed techniques preserve the original charging interval size, which may be defined for reasons of signaling efficiency, while simultaneously allowing the reservation or consumption of credit units from credit containers (36) having insufficient remaining credit for authorization of the full charging interval.