I have decided to leave my bv6000 and move on..
The issues were just too much in the end.
The speaker was just too quiet to hear the ringtones or SMS tones. I missed so so many calls over the months.
I have bought a letv s3 626 for half the price of the bv6000 and it is 5x better phone!
I'm sad to say my bv6000 wasn't up to the job. Taking calls is important for any phone and the speaker sucks.
The pros were battery and waterproof.
Cons: charging was often slow or didn't charge.. battery would be stuck at 1%..
The power socket (mini USB port) got loose and not well made.
Also big problem was delay in screen turning on. Sometimes 2 seconds to light up?
Basically too many problems for the price. Poor customer support and poor quality control.

Did you contact the seller?

I too will stop BLACKVIEW, I tested for 1 year and a half and therefore, not waterproof phone, NFC that does not work and it does not recognize the memory card. And now the updates do not appear anymore because you have to download them I do not know where.
Finished Blackview, Noel happens to offer me another brand.

My girlfriend has this phone more than 1 and half a year. The phone fall on the ground as many times you can understand. But there are some glitches : do not properly working ear speaker (replacement only few €), sometimes dont turn on - display problems viewtopic.php?f=142&t=319131&p=620466#p620466, loose battery (fixed).

I use mine for around a year and have no problems whatsoever. I may be lucky, but the phone is just fine. Now with the latest ROM of January 4th I am more happy with it than ever - finally the capacitive buttons work perfectly, and also other glitches apparently are fixed.

I had to replace the battery after a year (was swollen and worn out) and battery connector needed to be re-connected after it fell (normally the screen would have been smashed).

I'm using it for more than a year and a half now and although I'm overall pretty happy with its performance, I must admit I haven't been yet able to understand the way it really works and why...

Charging for example: sometimes done in 3h, sometimes it says it needs more than a day, which is usually reduced to some hours by either restarting the phone or flashing it a couple of times...
The same with stand-by time, can last to 1,5 days to 3-4 days without knowing exactly why the differences, since the use and the apps are the same...

Must point out the strange behaviours occurs with every ROM and updates available...

Any idea anyone?

Chinese smartphones, whilst cheaper than some of the bigger brands, have a few features built into them so that you remain reliant on their equipment, such as the 
stock standard BV6000 charger.   This is so they can make money of your dependency on their equipment.
This may be why you are getting slower charging times.  I noticed that the only way I can get fast charging speeds is to use the original 
USB lead and the original charger or a Chinese made charger.  Another USB lead with a long tip just doesn't seem to charge very quickly at all.  It's as you describe, very slow, can take over a day to charge.    But.. using the BV6000 cord it charges in a couple of hours. 

The other issue may be because you may not be using the original charger.  If the charger you are using isn't Chinese, then maybe it would explain why your charging times being slower. 

This article explains why this may be the case.   There is a difference between the European charging standards and the Chinese charging standards because this creates a dependency on  Chinese or EU made chargers, and may even enforce a manufacturer dependency..  

In some cases by bridging the two Data lines in your USB charging cable (at the phone end) helps improve the charging speed.  This YouTube video explains how to do this.

I would imagine, when there is little scrutiny of charging standards, any variations of this charging standard could be applied.  

Now.. having said all this, it may be that this phone could have in fact been made with European Standards in mind, not Chinese.. The reason I say this, is that the BV6000 charger is advertised as being of European standard.. That's not to say it is due to the fact that some Chinese goods are advertised as being U.S made when they aren't , but the Chinese charger I bought online (which I sometimes use for this phone) could also be of European standard so more people from overseas will buy it.  This may be why it works so well.

So the true test would be..  

• If it's of Chinese standard (then bridge your USB data leads)
• If it's of European standard (then bridge your USB data leads with a 200 ohm resistor).  
• If neither works, there may be some variation between the two.  Maybe a 100 ohm resistor, or a 500 ohm resistor.  I'm not sure yet but I will be conducting my own experimentsoon to try to get a solar powered phone charge to work with the BV6000.  Currently this solar charger will work on any other big brand phone but will not charge the BV6000.  The above could explain why. 

I really want this phone to work.. I really do, simply due to is rugged make and it's reasonable price.  I never agreed with carrying around a $1000 smartphone in my pocked.
However, I'm still ironing out all the tricks, and small issues like this which is preventing me from using it in the way I want to.  

I have tried calling Blackview in Hong Kong on Skype and if I get through to someone, they just hang up.  So I suppose it's up to us to resolve these issues through collaboration..
This range of phones are a great idea (rugged phones) but they have to be useable in all environments to be useful. 

All what you write tomithyom is related to HW, but doesn't apply in my case since I still use the original charger and cable.

Depending on the mood of the phone, charging can be completed in half a day, or just a couple of hours after a phone restart or flash, so it's purely a SW problem, not HW.

I had a similar problem when my cable was faulty.   That was when I was using the original charger and cable.
It intermittently speeds up and slows down the charging.

That could be the issue.  If not, you may need to replace the usb module in the phone. They're only around $10 so it won't break the bank. 
I've bought both the cables and the usb module on AliExpress quiet cheaply.  
Forget the warranty, with this phone the sellers simply wont' take responsibility for it, I've already tried. 

Have you factory reset it as well (just in case on the odd chance this is a software issue).