Having trouble with myiPhone 6 battery, it's not lasting very long under use. I realise that it's 3 years old now but I have 3 other iDevices that are older but still last a while. Anyway, I took it into a authorised reseller where they ran a test on it and told me that it had been "consumed" and could be replaced. I'd like to know what the test was as it was done out of sight, it took about 10 minutes. Is this something that I can run myself?