Steemers, I could really use some iPhone expertise right about now...

So my iphone has gone totally wack on me... (inb4 apple fagboy... I've enjoyed vanilla ios until now) My 400 dollar calculator started to die at less than 0% about a month ago.  This is an iPhone 5S that I recently received after punishing my old one with my reckless lifestyle and harsh working conditions (entertainment biz, stage crew, ect). 

 I assume it was a refurbished model so I did what is typically advised with new phones and just let it completely drain before charging it again... multiple times.  However, I feel my main err was not plugging it into iTunes, like ever.  

I just hate itunes... I really don't know why but the interface, its compatibility issues, the rampant updates and hellish TOS's that come out faster than any non DC Universe super genius could handle just makes me want to input some fist into the creators facial output source.   Anyways, time goes on and it begins dying at 30%... then 46%, 71%, 86%, 93%, 98% and bam I hit the point of no return, the hell that requires me to plug my phone into an external battery all day, making it look like I can't take a break from Pokemon go to recharge my phone.  

Then just yesterday it got worse, now even when plugged into an external power source i just get a loading apple screen for seconds, and then bam darkness for seconds... apple... darkness... It has become the metronome to my madness.  

PS: I've seen that this is a common problem for people who untether their phones.. i kept mine old school. WTF? So I did what any responsible google user would do and learned how to do a DFU reset, essentially a hard reformatting everything, a factory install.  It worked!  Except that I still need my external power source but I can look like a geek I've done it for years flawlessly.  I was ecstatic at my awesome repair job... I started download all my essential apps and for a few hours I was content with my pocket companion.  

And then it happened again...  boom apple... boom darkness... boom apple... boom.  What the hell do I do?  I just received this phone via insurance.  Should I say fuck it and just save up for an Android device?  Help me steemit, pls. 

EDIT: Itunes now wont let me do another hard reset... "An unknown error has occurred. (-18)" TF does that mean?