Increase in battery power typically increases your rate of fire by a noticable amount. Your FPS may go up, but don't expect a 300FPS to jump to 370FPS. You'll get a small boost (more power going through it). With more power going through it, you do run the risk of damaging your insides. I'm not 100% familiar with ICS's products, so I can't comment on whether or not a 10.8v battery would eat up the internals like hotdogs at a BBQ.
General consensus though, is that if you upgrade to a rather beefy battery, your internals should be upgraded to withstand the force of it.
Primary: Custom WE M16A3
Secondary: KWA MP9
Side: Custom WE M1911A1