That's true but still those batteries are significantly smaller than those of BEV buses - usually trolleybuses with batteries have 5-15km of range compared to 200-350 km of equivalent BEV buses which also means that the trolleybuses are significantly lighter than BEV buses, which helps with efficiency of electricity utilisation. Another efficiency factor is that not having to charge and deplete a huge battery will save quite significant ammnount of power that is lost as heat during battery operation.