Here is a picture of the battery packs I've collected, arranged from shortest to longest. The stock Ni-Cad pack is 5-1/8" long. The next one up is a McNair 3200 mAh NiMH pack at 5-1/4" long, and it fits snuggly into the HL battery box. The 3300 mAh pack next to it had to be forced in to fit. The other three do not fit.