[LG V20 Questions & Answers] br0adband:
Well GPS will drain battery when it's in use, as will anything related to location services if they're enabled (the Google Wi-Fi crap, the Lzat crap from Qualcomm - doesn't use as little battery power as it claims, and other aspects). While I can't directly account for what's killing your battery at 10% per hour, it might be a good idea to install something like AccuBattery (the free version does enough for that purpose), BetterBatteryStats (the full version can be acquired here in the thread for that app but it's worth the cost to support the developer), or Gsam Battery Monitor or something of that nature to keep an eye on what's going on.

If the battery you have it over 18 months old - an actual LG OEM battery will have the manufacturing date on the label - you might consider getting a new one soon. Also, my personal recommendation: don't fast charge the battery, use a traditional slow charger as often as possible and ONLY use a fast charger if you find yourself in a situation where the battery is really low, like 15% or less, and you really need to bump it up to 30/40/50% and get a few more hours from it.

I don't trust fast charging and I don't care what technology it uses or whether it keeps the cells nice and cool during the charging process, that's just my personal way of doing things. I use a traditional Samsung 2A charger 99% of the time I charge my V20 and the other 1% I might fast charge it using a Motorola "Turbo" 25 watt faster charger (QuickCharge 2.0 spec). So far with this particular type of usage with a "new" LG OEM battery I got last month, and charging it in the 40-85% range (AccuBattery alerts me when it hits 85% and I disconnect most of the time to extend the overall lifespan of the cells, not the per charge lifespan) and so far it's been great.

With the rooted Oreo on my V20 I see 0.2 to 0.8% per hour standby usage with locations services and Wi-Fi almost always on, even at home, and 4G LTE enabled too (I switch over to that sometimes to watch Netflix since with T-Mobile I can stream as much of that as I damned well please with no hit to my data). With Nougat and the same battery on this same V20 I was getting roughly 1.2 to 2.5% standby usage so it's definitely better with Oreo on it, at least for my usage patterns it is.

Good luck...

Oh, as for the hard reset thing, that's the general idea of a "factory reset," a wipe of the data partition and the cache and Dalvik partitions so the device on the next boot starts it's initial setup again as though it were fresh from the box. The terms hard reset and factory reset mean essentially the same things.

AND OF COURSE THE BEST POWER SAVING ADVICE IN HISTORY:

Don't max out the brightness all the damned time, seriously. Use auto brightness whenever possible or just manually adjust it, having it full bright is insanely ridiculous if you care about battery life in daily usage. I keep my V20 at about 40% at home, sometimes 50% when I'm watching Netflix, but the only time I ever go higher than that if in extremely well lit aka brightly lit environments like being outdoors and even then I don't go past about 85-90%, I never do 100% brightness.