Here are the differences "as posted" on the Surefire website:
KL1 mounted on the following torches:
E1/E1e Runtime: 16 lumens max output for 1.5 hours, followed by 8.5 hours of moderate output, followed by over 50 hours of minimal output
E2/E2e Runtime: 17 lumens max output for 4.0 hours, followed by 11 hours of moderate output, followed by over 50 hours of minimal output.
KL3 mounted on the following torches:
6P, D2, Z2, C2, M2 Runtime: 19 lumens max output for 4.25 hours, followed by 4.75 hours of moderate output, followed by over 50 hours of minimum output
D3, Z3, C3 Runtime: 19.5 lumens max output for 7 hours, followed by 8 hours of moderate output, followed by over 50 hours of minimum output.