Get -50V to 50V range from battery output
If you want to do this with a single SMPS circuit, you need some kind of transformer or capacitive coupling. You can do this with SEPIC topology http://www.linear.com/solutions/7345


TI has app note with transformer and capacitive coupling options for boost topology
http://www.ti.com.cn/cn/lit/an/slua288/slua288.pdf



Buck can also be used for this but obviously it does not apply here.

If you want a straightforward solution, use boost for +50V and buck-boost for -50V. You can often use buck converter as buck-boost, texas has app notes for a few different solutions. As a bonus this way both outputs are well regulated, dual output can have problems with cross-regulation.TI appnote shows you the efficiency and regulation suffers when you start draining more than 100mA.