Many important auctions---from spectrum rights to collectors' items on eBay---involve the same set of bidders repeated over time and bidders may face budget constraints in the course of auctions. We consider sequential auctions in which bidders have multi-unit demand, but are potentially budget constrained. For the case of two bidders with binary valuations and two auctions, we first derive the equilibrium to the second-price auction. In contrast to the standard static analogue, the auction involves mixed strategies in the first auction. The results are used as a departure point for deriving the optimal mechanism when the two auctions are independently conducted by separate designers. While the second auction mechanism is very sensitive to the amount of the bidders' remaining budgets a deterministic direct mechanism is employed. In contrast,  the optimal mechanism in the first auction involves offering lotteries to the bidders that assure that with positive probability a least one bidder’s budget constraint binds in the second auction.