On 4/30/2021 6:01 AM, Martin Gregorie wrote:
...

I didn't realise it has Li-ion batteries: using any power switch other
than mechanical is bad news for those: if you don't check their charge
state regularly the batteries WILL self-destruct if their voltage falls
below 2.5v per cell or they're charged above 4.2v. On top of that a Li-
ion battery self-discharges at about 2% per month, even when not
connected to anything.

If the Nano's charger (external or built-in) has an automatic cutoff at
full charge and can 'float' when the battery reaches full charge, I'd
leave it permanently on charge when its not being used. This style of
charger has been common for years for SLA batteries and is often supplied
with the device. My camera chargers (both built-in and separate) do this
and so does the charger for my Yaesu FTA-250 hand-held radio.


Right in theory, but in reality it seems that many of those
push-button-to-start devices hold their charge for many months, even
years, with no problem. I have several such devices, including rarely
used old smartphones and tablets, e-readers, goTenna gizmos,
flashlights, etc. The circuit of such on/off buttons can be designed to
use mere microamps *. LiIon batteries usually have a protection circuit
built in to prevent them from over-discharging.

The PLB I carry with me when flying has a push button to turn it on, and
its non-rechargable lithium battery pack is officially good for 5 years
- and then is still supposed to be strong enough to transmit (in pulses)
for 24 hours.

And I've read warnings in various places NOT to use a "float" charger on
lithium batteries. E.g., if you use a 12V LiFePO4 battery instead of
SLA in your glider (highly recommended!) do not leave it on a float
charger designed for SLAs when not flying. Ideally you'd use a charger
designed for LiFePO4, and it shuts the charge off completely when it
decides that the battery is "full". You can use a charger designed for
SLA, the battery will be mostly but not fully charged, and you should
manually disconnect it after it thinks the charge is done.

* Math appendix: if the battery capacity is 1 amp-hour and the
pushbutton circuit uses 10 microamps it will take 100,000 hours to
discharge the battery. That is more than 10 years.