And these would be the Battery Units! Modified and with the only purpose to satisfy and make their charger unit generate energy. They need to work together to stay charged and generate charge for the factory. They are imprinted in 2 models so they can compliment each other during the process, sadly once modified, this becomes their only purpose in life, same goes for chargers, and people have come to accept this reality given the eco-friendly energy the produce and how efficient it is for them to obtain, most cities run with horny energy these days, they just grew to accept people who decide to become chargers and batteries. Battery Units stay loyal to their charger and will constantly need for the charger to also feed them in order to stay active, if their energy lowers, they will start to get more "into it" as in, making the charger produce more energy, the lower the charge, the more persistent they become. If their energy is TOO low a direct connection from the charger to them is required, luckily running out of energy only shuts them down, so they don't run any harm. Batteries aren't cheap!

https://www.deviantart.com/soropin/art/Battery-Units-849735152