H1 uses the regular batteries in their grip. While H2 has rechargeble batteries that can power the digital back.
You can buy the rechrgeble batteries for H1, but it will not power the digital back, while H2 will. Of course this is applicable only for Hasselblad back. So if you plan to use a different back then Hasselblad, then don't bother with H2. H1 will do fine & save yourself $500 to upgrade.