Charging batteries doesn't add any load to the wires. But there is no restrictions on how much power they can take based on the power available from transformers. This means you can add a transformer to 20kw line, connect it to a pack of 5 batteries via 1kw cable. This will make them charge using all 20kw of power. The exploit would not be that much of an issue if by combination of automation and the transformer you would be able to send the power to a next circuit. This can be executed using two packs of batteries simultaneously. One pack has to be connected to the transformer input and disconnected from the energy source when the other has to be the other way around so it would be charging when the other pack is discharging. The wires from the batteries and the input of the transformer have to use appropriate wires, not the 1kw ones. Also the setup is not limited to 20kw as it's possible to connect as many transformers and battery packs as you want to a single line. You can see the setup on the screenshot. With consumption close to 2kw there is no overloading in any of the wires. Conductive wires is where the power consumption is actually can be 2kw.