70 and 100 Watt is not bad for smaller to medium size packs,, the Icharger 306b I have can put out 500watts on 12 volts,,, 1000watts on the 24 volt power supply,, I often charge 4-5000 4s packs at the same time (20 amp out put), takes just over an hour
Like I say,, pick the charger that fist you batteries size needs