On Sun, 9 Jun 2019 21:28:11 +0100, Nick Odell wrote:

On 09/06/2019 08:48, Archibald Tarquin Blenkinsopp Esq wrote:
On Sun, 09 Jun 2019 08:34:18 +0100, Another John
wrote:

Hi chaps,

A friend has loaned me his infrared binoculars (Nightfox) for a few
days, but the batteries (Eight! AA) are dead.

I have a supply of rechargeables, but these are NiMH and the
instructions for the device say "please use only alkaline or lithium
batteries".

Surely rechargeables would be OK? Or is there something terrible that
can happen?

Cheers
John

Yes.

The internal resistance of NiMh batteries is very low. High current
devices, flashguns in particular will be seen as almost a dead short
by a battery, An NiMh or a NiCad can deliver a lot of Amps from a
fully charged cell.

If the device is not yours, follow the instructions.

This.

I blew up the electronics in an "only use alkaline cells" camera by
using NiMh. A little discussion (either here or another newsgroup - I
don't remember) and it became obvious that the internal resistance of
the cells were critical to the performance and survivability of the
electronics. It was a 1980s camera so perhaps that design wouldn't have
been seen as so negligent in those days.

Nick

Could be voltage or internal resistance. I've a BP monitor that musn't have
NiMH - it has a little pump, so I expect the current would be too high.
Seems to me, in many cases, that the high-draw devices need the higher
resistance, e.g. so as not to overload a motor or, in the case of a camera,
the flash might be the critical circuit.
Oral-B toothbrush runs well on NiMH - one lasted just over 3 years, the same
as a rechargeable one that cost 3x as much. The Lidl equivalent needs the
higher voltage of alkaline.
I've a little Aldidl camera that's good on NiMH, so it's not all cameras.
--
Peter.
The gods will stay away
whilst religions hold sway