The 5945 is a good servo. Not a great servo, but a good one. Programmable, and can handle the direct output of an A-123. That is not high voltage. I ran them for quite some time on A-123's. The constant voltage of an A-123 isn't any higher than that of a 6v nimh after coming off a charger, and not much over a nimh after falling off the hot part of a charge cycle.
Just for laughs, I've seen people buy and install HV servos and power them with A-123's direct and be under the impression they were then running a "high voltage" set up. Not even close to true. The H.V. threshold is reached when running a 2s lipo, or 7.4v constant.