Re: (ET) New here, E15 and E12

["David Roden" <etpost drmm net>]

On 25 Sep 2021 at 0:01, David Tiefenbrunn wrote:

> LA any state other than fully charged accelerates their demise.  As
> long as LION are not over discharged, it doesn't matter much.

Totally correct about lead batteries.  However, a high state of charge DOES
matter with lithium ion, especially if you live where it's hot.

It's the opposite of lead.  When a lithium ion cell is mostly discharged,
it's in a relatively stable state chemically. There's no mechanism in
lithium cells that's anything like sulfation in a lead battery.  That's the
good news.

But when the cell is fully charged, the anode becomes highly reactive.
Especially at high temperatures, that causes the electrolyte to degrade.

Therefore a lithium ion battery shouldn't be left at 100% SOC, or close to
it, for long periods.

This is the reason that when you buy a new lithium powered gadget, the
instructions say to charge it before you use it.  That gadget probably
spent over a month on the ocean during its trip from Shenzen to Amazon.  :-
\  So it left the factory with a SOC around 50%.

The higher the temperature, the worse the full-charge degradation.  It
starts to have a significant effect on cycle life at around 80 deg F, and
becomes more serious at around 90 deg F.

I don't know about yours, but my garage isn't all that well ventilated.  It
gets HOT in there on summer days.  Even though I keep it at around 50% SOC
when I'm not using it, I store my e-bike's lithium battery in the house.

You can see how this could be a big problem for road electric vehicles.
Ask anyone who lives in the southwest and owned or owns a 2011 or 2012
Nissan Leaf about heat-related battery degradation.

The EV makers use a few strategies to handle this.  One is careful battery
formulation to minimize heat degradation, sometimes at the expense of other
battery attributes.  Another is active cooling, even using the vehicle's
aircon when necessary.

The main one is never charging to 100%.  Most don't go above 90-92% even
when the guessometer on the instrument panel says 100%.  A "50 kWh" EV
battery will usually be 55-60 kWh in actual capacity, but the car's
computer won't let you use that full capacity.  (I vaguely recall that at
least some Teslas may have had a way to temporarily use at least some of
this "reserve" capacity in an emergency situation, but I might be wrong
about that.)

A good strategy for long battery life in ANY lithium-ion-powered device is
to leave your battery at around 40-60% SOC after use, and charge it fully
shortly before you use it the next time.

One additional caveat applies to long term storage. Lithium battery BMSes
draw some small current from the battery, usually in the milliamps, all the
time.  Over a period of months they can actually over-discharge the
battery, especially if it's a small one.

For months of storage it's a good idea to disconnect your BMS, if possible.
 Don't forget to reconnect it before using the battery.

If you can't disconnect the BMS, as is often the case, periodically charge
the battery, then use about half of its capacity before storing it again.


David Roden - Akron, Ohio, USA

= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
Note: mail sent to the "etpost" address will not reach me.  To send
me a private message, please use the address shown at the bottom
of this page : http://www.evdl.org/help/
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =