I'm working on my PhD in materials science... but not in any sub-field related to batteries
Thanks for the info! I thought that my Li+ battery practices were "bad" (keeping my battery in my notebook when on AC power, recharging my phone even when the battery is not near completely used up, etc.), but apparently they aren't!
So, here's my question: with regards to preventing the battery from becoming overly depleted, what % is too low? I have used my battery on my phone until it hits 8%. Is that too low? It has a capacity of 1750 mAh, which is pretty much standard for phones these days, well at least for smartphones.
If it's possible to give a rough estimate of what charge levels could be damaging to a battery, I'd appreciate it.
Your phone will turn off above the safe minimum cell voltage.
If you then leave it off the cell will slowly discharge and eventually will drop below the safe voltage.
This is why it is suggested that if you're not using a battery for a few months you should leave it with 40% charge, and also why if you find an old phone that you've not charged for a year or so, the battery may never charge properly (just had to replace the battery in an old ipod due to it being packed away for the past 2 years).
When you charge the battery you're forcing current through it which produces heat and particulate buildup inside which reduces the life of the battery, which is why top up charges are better for lithium batteries rather than running the phone down to 0% and doing a long charge.