Living in a Sea of Lithium Ion Batteries

OK, "sea of Lithium Ion batteries" might be a bit of a stretch, but I'm living around a lot of them.  Within 6 feet of me there must be 10 of them.

For reasons that I don't recall, I was reading about electric bikes today and the topic of Li-Ion battery packs was being discussed, in particular keeping with the "polar vortex" cold weather this past week.  That led me to an article by Tesla on care and feeding of their batteries.

I was surprised by some of these, and figured since most of us use these batteries, it might be helpful to spread this around:

5. Leaving a battery pack at max charge for even relatively short periods of time can possibly affect its life. Lithium-ion batteries generally do best when they operate in the 30% to 90% range for state of charge.  In the context of an EV, if you're leaving on a road trip, you may charge your battery to 100%, but you should do that over the last hour before you leave so it doesn't stay at 100% charge for very long.  I can see no real equivalent for your phone, Kindle, or other smaller appliance, only a "sort of".  Perhaps you're going someplace where you expect to spend the day away from a charger and want to give the battery as much charge as you can.  Go ahead and charge it to 100%, just make sure you start using that charge in an hour, otherwise it might be better to just charge it to 90%.  More on that later. 

4. Conversely, leaving your battery in a discharged state for an extended period may also impact its life. What is a low state of charge?  Under 30% charge is generally considered low and thus you should not let your EV sit at that low state of charge for an extended period.   Similarly, you should not let your smaller devices go below 30% charge.

3. A lot of talk has been focusing on low temperature operation and how you should never try to charge a battery that's below freezing (0C, 32F)   The general rule of thumb for batteries of Lithium-ion composition is to keep the battery pack between 20F – 85F.   Both extreme hot and cold weather can impact performance for a battery with lithium-ion chemistry while lowering the discharge capacity.  Bayou Renaissance Man has a big article on this today, so more details there.

2. If you’re going away on vacation or for a business trip the best thing for your car is to set the charge level to 50% and leave it plugged in.  Still, leaving it at 90% is better for the battery (and you) than leaving it at 10% and coming back to find the battery completely discharged.  In the context of your personal electronics, I think this means to charge them to 90% and leave them unplugged from any charger.  If it has a real "off" mode, or lacking that an "airplane mode", use that to minimize battery drain and help keep the battery charge longer. 

1. Talking about their cars, which are much more complex than our small electronics, Tesla says a periodic max charge is helpful to your battery’s management system.  and they suggest doing this about once every 3 months or so.  I read it as the same might be true for our personal devices; charge them to 100% on the same schedule, and keep in mind that after you fully charge it you shouldn't let it sit; that would be a violation of battery management rule #5.

There's a trick question built in here: how do we know the % charge that our device shows is (1st) accurate and (2nd) the same percentage they're talking about?  Short answers for both (1) and (2): we don't  know.  A battery indicator in a phone is certainly a much simpler circuit than the battery management for the multi-thousand dollar battery in an electric car. 

Battery display on a Oukitel K6000 Android phone.  (Random phone chosen by image for that battery indicator in the corner)  Is that really 77% of the charge it can take or 77% of what they allow it to charge to?  Is it accurate within 5%? 

It's conceivable to me that a phone's software could already limit the charge to 90% of the possible capacity of the battery to help battery longevity, but tell you it's 100% charged to minimize "my phone doesn't charge all the way" trouble calls.  My gut feeling, though, is that the phone makers wouldn't do that because battery life is one of those things buyers weigh as important when buying a phone.  A look at some sample Android code doesn't seem to say they're doing anything other than reading the status as best they can and reporting it.

As I say, these bullet points were basically new to me, and I'm going to change my habits of how often I charge things.  I'm going to try to keep them in the 30 to 90% range and not let them go above or below that.  Both my 5 year old iPad and my two year old phone are acting like they need a new battery, and my tendency has been to throw the iPad on a full current charger and let it go to 100%.  It might be too late for these batteries, but it's something to try.