Everyone has their own opinion on this. Draining it below 10-20% could shorten the overall lifespan but I doubt the 80% or higher part you read is true. I personally charge mine every couple days and I'll still have about 30-40% left. I don't usually let it go lower than that. Rechargeable batteries like to be charged and killing them can damage them. Like a car battery, if it runs dead several times, it will most likely be ruined much earlier than if it wasn't ran dead. Just keep above 20% to be safe. Everyone's opinion of lowest percent is different.
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