The Energizer 376/377 is a high performance multi-drain watch battery. Multi-drain watch batteries perform equally well in low-drain and high-drain watches.
The size 376 and size 377 watch batteries are identical in size and voltage. The 377 is optimised for "low drain", while the 376 is for "high drain" applications. "High drain" means the bursts of power required e.g. when you press the light button on your watch. Because the 376 does everything the 377 does, and more, Energizer has streamlined production and now only makes one battery.