36v, 4.5A battery charging
It looks like Linear has some ICs that COULD fit your needs. But I haven't looked through the datasheet, so you'll have to check.

ICs I found are the LTC4000 and LTC4020 and at a first glance they look like they can handle high voltages and currents. LTC4000 has an external step-down converter, while LTC4020 uses four mosfets.

Here is the table I filtered on the Linear website. Curiously there are also LED drivers.. :?

http://www.linear.com/parametric/Battery_Charger_IC#!cols_1806,1112,1067,1068,1367,1069,1033,1032!s_1067,0!gtd_!1033_>=36!1067_>=8!1806_Lead Acid