Yes, you can. As a general rule of thumb you can always upgrade to a larger battery than what your light originally came with. The runtime will be extended by factoring the size of the battery pack.
Upgrade from 2-cell battery to 6-cell battery = 3x increased runtime
Upgrade from 2-cell battery to 8-cell battery = 4x increased runtime
Upgrade from 4-cell battery to 6-cell battery = 1.5x increased runtime
Upgrade from 4-cell battery to 8-cell battery = 2x increased runtime
We don't recommend downsizing your battery, e.g. Titan 4000 Lumens with the 2-cell or 4-cell battery. Operating a higher wattage light with a lower-rated battery is dangerous and doing so may exceed the current limits of the battery and trigger the protection feature to kick in.