On Sat, 20 Feb 2016 04:40:14 -0800, Phil Allison wrote:

RJH wrote:


Phil is right but I would wait until you have extracted it before
buying a replacement as it could be Ni-Cad or Ni-MH depending on the
age of the tuner, and they require slightly different charging
regimes. Equally it could be 3V, 3.6V or 4.8V although I would admit
that the size suggests the latter.


** AFAIK, Quad FM4s only ever used 4.8V NiCd battery packs with four
cells specially made for memory back-up. It was trickle charged at a few
mA whenever the tuner was powered up.

I doubt any re-engineering is needed to employ a four cell NiMH pack
instead.


Agreed, In fact, when I was looking for a replacement 3 cell NiCd for a
Potterton 2000 CH program controller, they'd changed to a larger capacity
NiMH version. Oddly, the tagless drop in batteries used by this
programmer were over twice the price of the solder tagged ones.

Naturally, I bought the cheaper tagged battery and pulled the tags off
and dressed the 'pips' with a fine file to recreate the plug in version
at less than half price for less than ten minutes of D-I-Y activity. :-)

The 4.8 volts seems unusually high for battery backed memory though. The
more usual with static cmos ram being 3.6 volts. CMOS sram is guaranteed
to retain data integrity right down to the 2 volt point - and that
includes the RTCs with their 70 8 bit registers 'going spare' as used by
IBM in their AT PCs first marketed back in August 1984).

--
Johnny B Good