Since having the device a couple of days, I have been measuring the charging. Unfortunately the 12 volt charging doesn't seem to work, 9 volt does but it wont go higher than 1500 mAh. I've tried multiple cables and chargers (different brands and charging protocols), but I cant get it to work properly. The result is the phone wont charge as fast as it should, charging from 60 to 100 percent would take about 4 hours. Is there any way to resolve this issue?

Did you use the Blackview charger and cable?