lg g3 marshmallow update & update via pc suite

hello ,, 1- i have lg g3 d855 i was afraid to use lg flash tool to flash the M is updating my lg via flash tool will get it into bootloop or similar things?
2- i checked for any new updates with lg pc suite then i found android M update available via it but im scared cuz i have a very weak connection its like 100-500 kb/s so its gonna take like 6-8 hrs to upgrade and ofc the mobile gonna be connected to my laptop ..
so i was wondering is it possible that my laptop damage my battery or...

lg g3 marshmallow update & update via pc suite

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