For that matter what is it with batteries that make them so fickle?
You can’t charge them to full, but at the same time you can’t let them die, but at the same time you should wait for them to die before you charge since constant charging is bad, but at the same time not charging enough is also bad like what’s the real deal with batteries T_T
In: Technology
batteries are sort of miraculous devices. there are only a few specific chemistries that are reliable enough that they’ve been adopted everywhere: lithium ion (phone), lead acid (car), and alkaline (AA), basically. this is 3 widely adopted out of thousands of potential chemistries. they are difficult systems to make work.
for why it’s bad to overcharge/overdrain them, there’s different reasons for different chemistries. you’re probably asking about lithium ion though, so it’s kinda like this:
to use a battery, atoms have to move across the battery. on either side, there are solid particles that can accept the atoms. this is a powder – on one side of a lithium ion battery it is literally powdered pencil lead.
the atoms in these particles happen to be structured such that they can gain and lose a certain number of atoms without the overall structure changing. you can think about a scaffolding, where you could remove some of the bars without the scaffold falling down, and add some bars as well, but too many or too few would cause it too collapse.
when you over-charge/drain, some of the particles lose or gain too many atoms, and the structure collapses and changes. when this happens, the atoms can no longer move in and out. the scaffolding has collapsed, and it is now difficult to remove a bar from the pile because it’s tangled up in the structure. atoms stuck on one side = fewer atoms moving back and forth = lost battery capacity.
that being said, as others have pointed out, advice to not leave things plugged in, not overcharge, etc, are remnants from before lithium ion. NICAD and NiMH batteries were used before lithium ion became the standard for lightweight, high performance uses, and they are far, far, far more tricky to properly charge. I can elaborate if you’d like. for long-term storage, it is indeed still better to store lithium ion batteries at medium charge and not plugged in. but for a battery that gets used even weekly it is not an issue.
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