Why do car manufacturers recommend only charging a battery to 80/90%?
In: 9
Batteries follow a charging curve – it’s fairly easy to put electricity into a battery when it’s nearly empty but it gets harder the closer to full it becomes. Think of it like packing a suitcase – the first few things you put in are easy, but at the end you’re sitting on the lid to try and get it closed. In general you can fill to 80% very quickly, but the last 20% will take as long as the first 80%. It will also generate more heat and waste more power.
Now that’s not to say you can’t or shouldn’t do it if you’re going to need the range – but unless you’re planning a road trip, for day to day use it’s cheaper for you and less stressful for the battery if you only top up to 80% over night. Save the ‘sitting on the lid’ charges for when you’re actually going to need those extra miles.
*All* (lithium ion) batteries should be charged to only ~80ish%. Many smartphones will have a setting that stops charging at 80%, and Windows 11 will discharge to 80% if it detects the laptop has been plugged in for a long time. Charging to full accelerates damage to the battery and reduces the lifetime more quickly.
I don’t know the exact chemistry of what’s happening, but I found an explanation [here](https://www.reddit.com/r/ebikes/comments/nzatsu/evidence_that_storing_liion_at_100_charge_causes/h1panws/)
Basically, heat is really bad for lithium ion batteries as it causes by-products that inhibit the chemical reactions that make the battery work. As the battery approaches full charge, the amount of reactants decrease, requiring more energy to force the reactions. That means more heat and therefore more by-products. Ultimately reducing the capacity of the battery.
For the same reasons, fast charging also causes more heat and more damage.
Thank you so much. I now understand. Couldn’t get my head around some other things I read.
It’s to prolong the battery’s life. Full charging puts more stress on the battery. It’s like constantly filling a water balloon to its max; it’ll pop sooner. Same concept.
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