Yes bob is correct, the charger is a 10a 100v power supply basically. So that would be equivalent to a 1kw so for a fully discharged 2kwh battery it would take 2 hours. And same with the 4kwh if it was fully discharged, it would be 4 hours.
We could do a 20a charger, but it might be a problem for some as you can use a 110v outlet, and some don’t have the 20a outlets, 15a is pretty common in the US. But if some of you guys want the 20a faster charger they are sorceable as that is what i used for awhile. Id did have a tendency to trip my breaker if I open the garage door. But i like this newer charger better as my routine is bacily fly in the evening, either plug it in over night or if i see the weather is looking nice the flowing day i plug it in after lunch. Or i leave it charged. Also this newer charger has a screen that show the voltage,amps, and indicating lights to show when its charged.
The charger is just a slightly more intelligent power supply, but you could use any 100v power supply as the battery does have its bms built in, and its rated for up to 80 amps of charge current. So you could charge the batteries up in 20mins for the 2kwh pack and 40mins in the 4kwh pack. But that wouldn’t be safe for the 2kwh pack as that would be over the max charger rating for the cell (which is 6A), So if you did have a very beefy power supply, the max time you could charge up the 4kwh pack would be 40mins will still being under the manufacturer’s safe rating. (you can see specs here https://cdn.shopify.com/s/files/1/0697/3395/files/samsung-40t-datasheet.pdf?6001754416888422053)
Now I wouldn’t recommend that as that would decrease your cycle life a lot, so that is why i think the 10a as a sweet spot, as it maintains battery health, and isn’t too slow as to get annoying and is compatible with most households.