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Iphone has been through 5 battery replacements(I kid you not) so far. When i let the phone die for as little as a day the battery goes flat and the phone refuses to turn on. Is this another issue, or is it just a matter of sheer bad luck of the batteries im receiving.

That’s another issue for sure..either a short but not very likely according to your problem description or most probably a battery charger circuit issue that needs an IC replacement on the logic board. That would be a bit expensive and might not be economically viable on an iPhone 6 nowadays, unless it’s one with a larger storage. If you have a reputable microsoldering lab in your area you can ask for a quote, they’ll know what needs to be replaced and might be willing to the job for an affordable price.