Key Features For SK 6000 and SK 9000 Transmitters Rechargeable Lithium-Ion 6.5-Hour Operating Time The Sennheiser BA 61 is a rechargeable battery pack for the SK 6000 and SK 9000 bodypack wireless transmitters. It provides up to 6.5 hours of operating time on a full charge. To recharge the BA 61, the L 6000 charger and LM 6061 charging module (both available separately) are recommended. As an alternative, the L 60 charger can also be used.