Might be low voltage (only 1.2V nominal)/low internal resistance of such cells.
I bought Lidl's blood pressure monitor and that had the same warning with no explanation - unlikely to be children involved in 'playing' with it.
Some of my clocks will run for 9 months on NiMH as they dip out at about 0.9
- 1.0V but others pack up at appreciably over 1.2V.
I noticed that the LED conversions for Maglites etc. mentioned on here last week gave the run time for the LEDs based on NiMH. It's about time all devices could run on either.
My guess: because it's too easy to short out the battery by mistake. With a rechargeable cell that could result in a dangerously large current flow, resulting in burns or a fire. Primary cells tend to have a higher internal resistance and are less likely to pose a safety hazard if shorted.
Usually because the low internal resistance of rechargables can allow too much current to flow in certain devices. It is particularly easy to kill some cheap flash guns stone dead by repeated charge and fire cycles when rechargables are fitted. Slightly less voltage but higher currents flow and the thing self immolates after a while.
The other failure mode is that the terminal voltage of a rechargable is slower than an alkaline secondary cell and so can look to some low current devices like it is spent prematurely.
There are products where the self discharge rate of most rechargables compared to secondary cells makes them less than useful. I have a collection of used at high current secondary cells that still have enough life to power digital clocks etc. I usually end up on secondary cells after a set of "charged" rechargables have failed to deliver.
I am gradually swapping over to low self discharge types but have a fair proportion of older NiCd and NiMH (even some NiFe at my parents).
I measure the voltage of a spent cell and note it on the back of the clock, then write the date on the 'new' cell. Cells from e.g. the CH controller still have 1.4V and that sort of thing I note the voltage, keep them in a separate box and fit them to the clocks that'll go to low voltage.
All of mine are now Eneloop or Aldidl LSDs, somewhat helped by the ordinary NiMHs failing quite early.
Well can only guess that if it seizes up and takes a lot of current rechargeable batteries will trash the device.
Of course it should be also borne in mind that most rechargeable as you normally get in dry bat sizes are a quarter volt lower in voltage so some devices might not like this much. Brian
I am the grandfather and the toy has 2 batteries mounted in series to give 1.3 + 1.3 = 2.6 volts to a loop that has
1 LED light
1 resistor
1 buzzer
Now I have removed one of the batteries and by clever new assembling found that the loop gives sound and light also by using only
1 rechargeable battery that has 1.3 volt.
If I show this tool to my two grandchildren (2 boys of age about 12 year and 7 year) I will tell them that rechargeable batteries are used, and should always be used for such a tool.
I will tell them that they live in a world where evil capitalists try to fool them and I will show them how to fool the capitalists by running the toy on cheap green energy that is friendly to mother earth.
Please don't. As has been pointed out, there are sound reasons why rechargeable batteries may not be appropriate (including safety reasons) so you don't want to give the impression it is OK to ignore a warning.
NiFe are also incredibly robust - bordering on indestructable.
I have a couple of still serviceable blocks of ~40Ah from fork lift truck units made redundant in about 1970. The KOH caustic degrades after a while but that is the only maintanance they have ever needed. The replacement forklifts have since burned through over a dozen sets of NiCds (partly by incorrect charging regimes in the early days).
The manufacturer of that silly toy did not do any calculation of LLE He simply put in a lot of warnings because they may be of help if a customer sue him after an accident.
I have already shown you this warning:
and there are 8 more:
Do not mix old and new batteries
Do not mix alkaline, standard (carbon zinc) or rechargeable (nickel cadmium) batteries
Exhausted batteries are to be removed from the toy
Non-rechargeable batteries are not to be recharged
Only batteries of the same or equivalent type as recommended are to be used
Batteries are to be inserted with the correct polarity
Do not dispose of batteries in fire, batteries may explode or leak
Batteries may explode or leak if misused
Risk evaluation is very important. Let me show you the proper way to do it. I have memorized this LLE-table and tell it to anybody that want to listen to me:
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OF LIFE EXPECTANCY (LLE) DUE TO VARIOUS RISKS Activity or risk* LLE (days) Living in poverty 3500 Being male (vs. female) 2800 Cigarettes (male) 2300 ... 15-lb overweight 450 All accidents* 400 ... Occupational accidents 74 AIDS* 70 Small cars (vs. midsize) 60 Married to smoker 50 ... All electricity nuclear (UCS)* 1.5 Peanut butter (1 Tbsp./day) 1.1 Hurricanes, tornadoes* 1 Airline crashes* 1 Dam failures* 1 Living near nuclear plant 0.4 All electricity nuclear (NRC)* 0.04
Whenever I see a fat fellow that is smoking I become very glad because I am slim and do not smoke.
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