The more batteries, the more energy
Wrong Track: Adding batteries gives more energy to the charges.
Right Lines: The charged particles flow at a greater rate and the bulb is warmed more by their working–just like the rope loop being pulled through your hands at a greater rate when I pull harder.
Adding batteries makes the bulbs glow more
Thinking about the learning
The idea that adding batteries increases the rate at which energy is being supplied to the circuit makes intuitive good sense to most pupils.
However you should avoid any temptation to suggest that the charged particles are
given more energy. They are not. The rope loop is very useful here, as it correctly presents the idea that what is going on is a kind of remote working. The electrical loop links the shifting of energy from the chemical store of the battery to the shifting of energy to the thermal store of the surroundings as the bulbs glow and the radiating warms their environment.
Thinking about the teaching
The rope loop model is likely to be useful here in helping the pupils to picture what is going on:
Teacher: So, with the rope loop, I worked harder to pull the rope around with a bigger force. I seem to remember that Anita felt the benefit of my efforts as her hand warmed up. It's a good job I didn't have to keep going for too long!