It appears that your son was given the regular DPT +OPV shot and hence the fever
The fever due to vaccination
will settle down in 3 days.you can give him painkillers like paracetamol
to relief his fever and pain.You could also do cold sponging at the area of injection.
You could also opt for painless vaccine
next time which leads to no fever and pain post vaccination.
Power issues can be sorted out by using invertors/generators at home .