On 02/02/2020 13:34, Andrew wrote:
On 02/02/2020 09:55, The Natural Philosopher wrote:
On 02/02/2020 09:43, Andrew wrote:
Turned on the ancient Sony FM portable this AM and noticed
that the red tuning LED was not coming on even though the
signal seemed ok.

It runs on 4 rechargeables, currently a set of 2008 Eneloops
which were recharged about a week ago, but have only been in
use in the radio for couple of months (normally used in a Ricoh
Caplio camera)

Out of interest I took them out and measured the volts.
Out of the 4 batteries, two (inline) measured 1.29 volts
while the other two measured MINUS 0.094 volts !!??.

What's going on ?.

For some time I have noticed a strange, faint drum-beating
sound from the radio even when it is switched off.

Elves inside trying to get out.

driven into reverse charge by the better cells

Not unusual

It was a set of four that have had similar usage.

In any set of four there is always a weakest cell. The first one to fail
will have current flowing through it driven by the remaining good ones.
Leakage is often a problem if the cell is abused in this way for long.

Devices that will tolerate a wide range of input voltages tend to cause
this sort of problem most often. Many higher current devices have an
absolute minimum voltage where they will work and shut down gracefully
to avoid driving any weaker cells into reverse bias. LCD based kit tends
to self limit when you can no longer read the display on it.

--
Regards,
Martin Brown