Have a Milwaukee string trimmer. Came with a 9AH battery. Plenty for our .6 acre. Have a 2.75 acre with fence. Had to buy a 12 AH battery and between the 2, my wife can about get it done. Plenty of power.
Blowers, I have 2. One is an 80 volt Works and it blows well. Battery life is good for 3 times or 4 of blowing off the driveway which my wife covers with grass
Other is an 18 volt Ryobi that is adequate.
4ah battery may be a little light for a trimmer but fine for blower I would think