Yep, all Ego chargers, batteries and tools are compatible. The only condition is that some of the larger tools require the larger batteries to perform at maximum power. The snowblower for example required two batteries at least 4Ah or larger, but will run on smaller batteries just at a lower power level.
Actually the EGO snow thrower will run on only ONE battery in one of the bays. And there is no observable difference in throwing distance or 'snow moving power' whether there is only one battery installed or two batteries. At least that is how my unit appears to work since I bought it brand new.
The battery will draw up to the amount it's designed to draw, so if the stock charger only supplies 75% of that much current, it'll take longer than it should to charge. If you use a charger with more current capability (and that's the key - it's only capability - it doesn't force that much current through your phone), the battery will charge at its full rated current, so it charges faster. You could use a 10,000 Amp charger - as long as it's 5 Volts and has a microUSB connector on it - and the battery will still draw the 1 Amp or so it's designed for.