Huawei honor 6 restart problem

Big problem with Huawei honor 6 handsets. After updating to EMUI 3, phone continuously restarting. When forwarded to service center, they are saying battery problem. And even after battery changed, the restarting problem exists. I have more than 5 honor 6 phones with the same issue, only after updating EMUI. I don’t think all of these will have battery problems that to of a sudden.
When we switch it on, it immediately restarts and again and again till battery drains completely. Can anyone tell me a solution to this? And is there any way to downgrade EMUI as the phone is not in on condition?