A general rule for not charging a lithium ion battery beyond 80% of capacity. Whether smartphones or electric vehicles (EVs), keeping the battery above 30% and under 80% has been known to preserve battery life. In fact, late-model iPhones and Androids have a setting to stop charging at 80% or 85%. For EVs, DC fast charging all the time is also known to lower battery life. See
lithium ion and
EV charging.