Hi,

So many times i read in product manuals "dont mix old and new
batteries", can someone tell me why?

I have a wireless mouse and keyboard here and strapped for cash. Got
some nice energizer batteries and i want to put one in the mouse and
one in the keyboard. Each take two batteries each, any harm in mixing
them up?

"Sir Psycho" wrote in message
ups.com...
Hi,

So many times i read in product manuals "dont mix old and new
batteries", can someone tell me why?

I have a wireless mouse and keyboard here and strapped for cash. Got
some nice energizer batteries and i want to put one in the mouse and
one in the keyboard. Each take two batteries each, any harm in mixing
them up?


The BIGGEST issue I see is the old one will wear out first, causing more
battery changes aand in the long run being more expensive than if you put
just new batteries in to begin with. There may be safety issues, I guess. I
am just looking at efficiency issues.

On 2 May 2006 05:55:47 -0700, "Sir Psycho"
wrote:

Hi,

So many times i read in product manuals "dont mix old and new
batteries", can someone tell me why?

I have a wireless mouse and keyboard here and strapped for cash. Got
some nice energizer batteries and i want to put one in the mouse and
one in the keyboard. Each take two batteries each, any harm in mixing
them up?

Sounds like you could put two older batteries in one or the other
mouse/keyboard . . . .

I know of no real reason for not mixing batteries except it is false
economy to take a new battery and put it with a near dead one - weak
ones have higher internal resistance and power from the new one will
be wasted warming up the older one. In a large battery pack, in a
high current application, that warming could be significant - but two
batteries, in a mouse or keyboard? No.

The old one may be prone to leaking and ruining the device . . .

The old/new mix will make it look as if the device eats batteries even
though with fresh batteries it will last awhile. Customer doesn't
always remember they were mixing batteries.

They may be covering their corporate asses and playing it safe.

I have an mp3 player that eats its single AAA battery in about four
hours - I put them (any brand) in the recharger (by Rayovac for their
NIMH and alkaline rechargables) and they are good to go for another
four hours - I can do that about 6-10 times then they start failing in
a couple of hours and are prone to leaking. I use it every day,
recharge every other day, so I have a good feel for how it is working.

Same thing works with alkalines for clocks and remote controls etc..
Get a little more life out of them . . . Just watch for leakage


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The main reason is he the combined internal impdance of two batteries.
Connecting 2 batteries in series make the total impeadance as a sum of
each so if the load consumes certain current the voltage will drop to
the unsustainable level by power supply of the unit.
The new alkaline battery has ~0.2ohms(good ones). The old one has
1ohms. So 2 new ones may have 0.4 and old and new ones 1.2. The new battery voltage is ~1.5and the old one is 1.2V (open circuits) so 3V/0.4=7.5A or 2.7/1.2=2.25A of short circuit currents.
There could be certain conditions of batteries internal impedance,
their voltages and load impedance that creates reverse voltage on older
battery resulting in quicker damaging that one. It is specially
possible with pulsed load. So as for your loads (pulsed one) it can be
more critical than for torch.

Another reason is that old battery has lower Ampere-Hour rating
(because it is used). And when they are connected in series, the new
battery will be wasted because the maxium AH is limited by that of the
old one.

Reference:
http://www.kodkodkod.com/files/ampere_hour_rating.htm

KodKodKod Learning Consulting - Here you get the answers! @
http://www.kodkodkod.com

On 2006-05-02, Sir Psycho wrote:
Hi,

So many times i read in product manuals "dont mix old and new
batteries", can someone tell me why?

it can cause the depleted cells to become "charged" in the reverse direction

(if you don't understand how that could happen i'd suggest studying basic
electronics, in particular kirchoff's loop law.

that can make them leak, or worse...

I have a wireless mouse and keyboard here and strapped for cash. Got
some nice energizer batteries and i want to put one in the mouse and
one in the keyboard. Each take two batteries each, any harm in mixing
them up?

could leave an ugly stain. may damage thje insode of the devices too.

maybe you can do without the mouse?

--

Bye.
Jasen

I just test my used batteries with a voltmeter ( very inexpensive these
days) and pair according to voltage. The messured voltage seems to drop
steadily as they are used .-cougar

On Fri, 12 May 2006 08:03:26 -0700, (Joe
Cougar) wrote:

I just test my used batteries with a voltmeter ( very inexpensive these
days) and pair according to voltage. The messured voltage seems to drop
steadily as they are used .-cougar

---
That's exactly as it should be.


--
John Fields
Professional Circuit Designer

"John Fields" wrote in message
...
On Fri, 12 May 2006 08:03:26 -0700, (Joe
Cougar) wrote:

I just test my used batteries with a voltmeter ( very inexpensive these
days) and pair according to voltage. The messured voltage seems to drop
steadily as they are used .-cougar

---
That's exactly as it should be.


It's much better to measure the voltage on load.

That is connect a resistor across the battery chosen so that it passes a
current similar to the device the battery will be powering and then measure
the voltage.

--

Brian Gregory. (In the UK)

To email me remove the letter vee.

Sir Psycho wrote:
Hi,

So many times i read in product manuals "dont mix old and new
batteries", can someone tell me why?

I have a wireless mouse and keyboard here and strapped for cash. Got
some nice energizer batteries and i want to put one in the mouse and
one in the keyboard. Each take two batteries each, any harm in mixing
them up?

Yes...the new one can (eventually) attempt to "charge" the old one and
cause it to leak...and prematurely discharge the new one. Put both new
cells in the same device and both old ones in the other device. If you
are so strapped for cash, find you wired mouse and plug in into the
appropriate port.