In reply to Tobes:
> Doing a quick Google cross reference, looks like the 2ah can be used in the trimmer but with a ‘degree’ of loss of power and run time.
Simplistically a 2AH battery contains 2/5ths of the energy of a 5AH battery (assuming like for like voltages) so you'll get something like 40% of the runtime, a bit less in reality for reasons not really worth diving into. Power loss should be negligible given they're broadly comparable sizes and should have broadly comparable internal impedance.
The issue is why does the hedge trimmer ship with 5AH batteries to begin with, it may simply be that in recent years prices have fallen so they're now the default, it may equally be it's a power hungry machine and needs the big battery to make it a practical tool with a worthwhile runtime.
There is a risk of overloading low capacity batteries, like for like chemistries and structures will have a 'C' rating, a multiplier of capacity. If for example the batteries have a C rating of 5 you can draw 5x5 = 25A from the 5AH battery, fine if your clipper draws 15A. However we can see there's a problem with the smaller battery, 5x2 = 10A which is less than the 15A your clipper draws. The best case is tripping protection, the worst case is rapid battery damage and potentially with poorly designed packs, fire.
End of they day you can but see how others have got on or try it.
jk