Is Nando's halal?

So here in the UK there are two types: you have the branches which are halal and the branches which are not halal. The halal branches where the controversy has come in the past is that they use meat which has been stunned initially. Now the question is then: is stunned meat, is that permissible for us to consume? And as long as the voltage used in the stunning is low, meaning that it would not kill the animal, and the animal is then slaughtered islamically, then that meat would be halal. So that would be the general principle: as long as the voltage used would not kill the animal. So, for my understanding, previously the voltage was higher and there were animals that were being potentially killed, but now the voltage is so low that it would not kill the animal, and therefore as long as it's slaughtered after that islamically, then the meat would be halal.