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
Surely rechargeables would be OK? Or is there something terrible that
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.
Don't be a cheapskate, your mate has lent you the bins the least you can do in return is put the correct batteries in and think of the brownie points the next time you want to borrow summat off him again!
On 09/06/2019 08:48, Archibald Tarquin Blenkinsopp Esq wrote:
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.
On Sun, 9 Jun 2019 21:28:11 +0100, Nick Odell wrote:
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.
I'm an ignoramus on electronics but I can measure the current drawn by a
blood pressure monitor and calculate the likely effect of using
batteries with lower internal resistance but also lower voltage. So,
despite the manual having "Do not use rechargeable batteries", ours has
worked happily on NiMh got 6+ years.
There is perhaps a third course: ask yourself if the manufacturers are
just (a) covering their arse and (b) deflecting the prats who send stuff
back as faulty when it doesn't work 'cos they've stuck in flat batteries.
reply-to address is (intended to be) valid
I would not expect any normal electronic device to rely on the batteries
having a certain minimum internal resistance, and to disastrously
malfunction because it was 'too low'. I would have thought that it's a
case of 'the lower the better'.
As has been pointed out, the obvious problem is that rechargeable
voltages are lower than their non-rechargeable equivalents. I have a
camera and a DAB radio that both need at least 1.3V, and fully charged
Nicads and NiMHs (which rapidly drop to 1.2V) don't keep them going for
If it is something that is regulated to deliver either constant power or
constant output voltage when the input voltage being too low combined
with the very low internal resistance of rechargeable cells results in
frying the device. Old cheap flashguns were very prone to this failure.
The things where damage can result are typically drawing a fairly large
current from the batteries and relying on their internal resistance to
limit the current into the device. It used to be quite a common trick.
Low current devices fail gracefully on rechargables with insufficient
voltage to drive the LCD display to decent contrast.
Another reason for the 'no rechargeables' disclaimer might be the
self-discharge on NiMH. It's no good if an infrequently-used widget is
always flat when you come to use it - and the manufacturer will probably get
the blame for flattening the batteries.
These days we have low self-discharge NiMH so this problem is much less, but
perhaps the manufacturers still put the disclaimer in because people will
use non-LSD NiMH and then complain.
I've a couple of DAB radios that work fine on rechargeable NiMHs - about
the same life as alakali. Despite the manual saying not to use them.
Mind, a DAB radio isn't exactly high current. Nor I'd have thought the
I would expect this problem to occur with equipment which needs a very
high input current, for instance to charge the capacitor in a flash gun
as quickly as possible for a given size of battery, and to get the best
possible result from alkaline batteries has no intervening circuitry to
limit the input current. It would presumably be fairly easy to design
it so that the highest possible current even from an outlier among
alkaline cells was ok. But then a new cell type with available short
term current 10 or more times higher might fry the input circuitry. I
have not seen this myself but it makes sense
On Sun, 9 Jun 2019 09:43:24 +0100, "Jim GM4DHJ ..."
Voltage shouldn't be too important within reason. Any device that
stopped working at 1.25 V would "waste" a lot of bettery power with
Generally outdoor "toys" have to have a bit of resiliance regarding
Volts anyway, simply because low temperatures can drop the applied
A low source impedance can mean disaster for equipment as a lethargic
oscillator will sink a lot of Amps.
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