How To Charge a Battery in Falstad Circuit?
Battery in falstad is just a voltage source, so you could put 2 voltage sources in a series - one larger than the other, and the plus side of one next to the plus side of another: - + + -.
Then the current passing through the second voltage source will be charging it.
The way you know it’s charging is that there’s a voltage drop across the 2nd smaller source in the direction of current flow. That voltage drop represents the energy the current loses to battery being charged.