The Large NiMh Battery, BMHL is the kick butt size so it's a popular option for all day shoots and high power venues. Many people consider this Battery the biggest that they want to carry and it gives them 450 flashes per charge at 200ws so it is no slouch.
It gets 50% more flashes than the NiCd Large Battery so that's an extra 150 flashes per charge for only weighing a few onces more and in the same size as the Large Nicd. For all that extra performance the NiMh version is only $50 more expensive so the BMHL is the best value as far as flashes per dollar of any size or chemistry.
It's a good idea for photographers to have two or more batteries, but if you want one that has mega amount of flashes per charge, start with the Large sized NiMh Battery. If you do wear it down, you can swap it as easily as any other.
If you use 200ws we guaranty 450 flashes per charge. If you use 25ws, that same battery gives you 2400 flashes. Likewise, if you use only 400ws, you should expect 225 or more flashes from this Large sized Battery.
The NiMh Batteries all have a Four Year pro-rate warranty on the cells. For the Large Battery, that warranty loses value at the rate of: Full coverage in the first year, 25% in the second year, 50% by the third year and 75% for the fourth year and full price after that.
In some cases, there may be a sale price that is a better value than the total pro-rate at the end of the warranty. There is a small labor fee to install the cells and new cells always start a new pro-rate warranty. The case and electronics have a Two Year warranty from when it's originally purchased.