Companies itching to IPO are braving the markets again. This morning, Rackspace had its IPO (RAX) and today nanotech battery company A123 Systems filed its IPO registration document [an S-1] with the SEC. The Boston-based company is hoping to raise $175 million in an IPO. (It’s already raised $132 million in venture funding from Sequoia, General Motors, Motorola, Qualcomm, and others).

A123 Systems makes next-gen lithium ion batteries for electric and hybrid vehicles, as well as for smaller portable devices. It is working closely with GM and Black & Decker. The company, which came out of MIT, already employs 1,100 people (150 in R&D alone), and has been manufacturing batteries for two years. The company’s revenues in the first quarter of 2008 was $10.3 million, and its sales for all of 2007 was $41.3 million. It’s also been eating through a lot of cash. Last quarter it had a net loss of $14 million, and last year it lost $31 million.