Motor power (watts) is a product of volts times amps (current). Power loss in the motor's windings is a product of the current flowing against the resistance of the wire. Increasing the voltage gives higher power without increasing the resistance loss. For the same power, higher voltage uses less copper or aluminum wire in the motor, has less heat loss, weighs less and is less expensive to make than a motor of the same power running on less voltage.
I have an EGO string trimmer, one of their first models. I've taken the battery pack apart, and found that EGO uses a thermal wrap around each cell to help keep them cooler, both in charging and in use. I believe this is why the battery pack has lasted so long, and can deliver a lot of current as needed. Turned out the problem was with the outlet the charger was plugged into, so put pack back together and still use it.
In the other brands of battery packs I've dissembled, the batteries are packed close together, making thermal degradation of the cells more likely than in EGO's packs. This also limits how much current they can safely supply for the given amount of cells. Kudos to EGO!
