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