First off you will never come out ahead. If you have a thousand watts its just going down from there from countless electrical losses. Its best to build the battery bank to match the operating voltage you need or find a different motor for your needs vs power supply.
Second, batteries have a limited voltage for their operating range and the more depth you use of that the short their lives will be. Sure you can use a transformer or puck converter to suck em to zero voltage, but it will never hold a charge again.
