Mike,
Worry about the low voltage instead. The ICU is designed for LiPo cells! So if you want to use different cells, be sure to meet the low voltage requirements with whatever cell type you choose to use (LiPo low voltage cut-off). The Lipo High voltage for the type (L,S,P) is safe. If You use different batterie types, use in line high current diode(s) to take the excess voltage as compared to LiPo and cross check against the expected low voltage limits.
That way you will play safe, But am sure you already knew that? Then there is the quite standard 10% excess voltage upper margin as in all electrics. Use that at your own risk though.