You got the currently most popular package. If you want to downgrade to a F4s or F4e, you would even get some cash out of it.
Originally, the F4s accounted for the vast majority of sales (plus some F4e among professional users requiring external power supplies or rechargeable cell blocks). By now, the F4 (with MB20) has grown into the most popular version, and sells for more then the F4s and F4e - thanks to lower size and weight and the dwindling need for high frame rates in a film camera. The MB20 by itself sells for something like half or two thirds the price of a entire working F4s...
If you want one of the bigger packs, stay clear of the F4e/MB-23 - its main purpose was quick recharging of the entire battery block (plus powering the bulk film back and attaching a external power supply), but it depended on the now abolished NiCd cells (even if you rebuild a pack, the Nikon quick charger will cook modern NiMh cells). So you are left with a heavier, less handy pack that has to be pulled apart for charging just like the F4s, and whose (MS-23) battery holders are scarce as hens teeth, so that you may be stuck with the (usually dead or at least very flat) NiCd battery module.