9Volt vs. AA Recheargeable Batteries

[missmoo]

Hello,

I'm not quite an electrical engineer (YET! but I do some of this as a hobby as I get my degree. I have a question I need assistance with, hope you can help me.

At my job we are working with magnetometers that are powered by a pack of 7 AA batteries (Rechargeable) encapsulated in a pack that has a 9v type connection to the circuit board. One of those devices is connected to a simple 9V rechargeable battery instead of the pack.

The batteries are at terrible shape (due to neglect and bad maintainance of the devices, mostly) and we are about to change them all. As the only person that knows half a thing about electrical currents and circuits, the job of choosing the replacements fell on me.

My question is this: Which type of rechargeable battery is better? The 9v or a pack of 7 AA ? which would hold out longer, or which would survive longer? Is there really a difference?

I apologize if I don't supply information that is relevant, I don't know much about batteries. If you need more information, please ask. I also apologize if this is in the wrong forum. Again, I'm doing this as a Hobby, and try to learn in the process.

Thank you very much,

Moriel

 

[IRstuff]

Well, it time that you apply some engineering analysis to the problem.

Assuming a constant energy density, would a larger volume produce more total energy?

TTFN

FAQ731-376

 

[Skogsgurra]

As IR says.

I usually go from 9V to a set of AA. Not AAA.

AA has come to be THE battery used in most applications. It is THE battery that has a good combination of volume, capacity, price and longevity.

I even choose cameras and similar things based on batteries. If not AA, then I evaluate AA battery devices first.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[logbook]

How many battery packs are you talking about changing? If it is tens of them then maybe you should look at a battery analyser/charger/ from somewhere like Cadex.

http://www.cadex.com/

You may be able to repair the batteries by a suitable charging method.

On the other hand, if the batteries are 5 years old you will get at least double the energy capacity by using new ones, simply because energy densities have improved dramatically in this period.

Comparing battery packs you need to compare run time, weight and cost. This will allow an informed decision.

 

[zeusfaber]

Keep at the back of your mind that if these are NiCds, there is quite likely to be a difference in technology too.

Last time I was interested (at least a decade back, so treat with caution), PP3 sized NiCd were still mass plate technology, compared with AAA and bigger which had all moved on to a sintered construction.

The sintered technology tolerates much faster charging, and from what I can remember, had a better energy density.

A.

 

[zappedagain]

Batteries are rated in amp-hours (or more like mAH, milli-amp hours) to determine how long they will last. For example, a typical alkaline AA cell has a 2700 mAH rating and a 9V has a 565 mAH rating so at the same current draw the AA will last over four times longer. That is the specification you want to start with when deciding what battery architecture to use.

Go to

http://energizer.com/default_refresh.asp

and check out the 'learning center' and 'technical info' pages.

 

[MikeHalloran]

The disadvantage of a stacked battery like the common 9V is that you can't access an individual cell for diagnosis or electrical rejuvenation.



Mike Halloran
Pembroke Pines, FL, USA

 

[Noway2]

One thing that I learned recently, is that 9V batteries are pretty much reserved for fire protection equipment, such as smoke detectors. Apparently, this was written in to 'code' along the way. The problem was that several years ago, when hand held video games that used 9V batteries became popular, kids were removing the batteries from devices such as smoke detectors to power their games.

 

[MacGyverS2000]

That's a pretty enterprising youngster to know that 1) a smoke detector uses a 9V battery, 2) he goes through the trouble of getting out a ladder to remove it, and 3) the parents don't realize something is up when they see their child screwing with the detector. Maybe one kid did it and an urban legend was born?


Dan - Owner

http://www.Hi-TecDesigns.com

 

[Skogsgurra]

On the other hand, Dan, youngsters tell each other about such things. Getting batteries for their games seems to be a constant problem - getting them for nothing is probably irresistable. And, also, given today's ceiling height, they do not need a ladder - only a stool or something. Kids aren't four feet tall for many years.

But, then again, the Urban Legend part of it is intriguing - anyone with first-hand information?

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[VEBill]

"...9V batteries....reserved....smoke detectors....written in to 'code'..."

Hmmm... Smells like an urban legend. Is there a reference anywhere?

9 volt batteries are still very commonly used in clock radios for back-up power.

 

[MacGyverS2000]

TV remotes were often 9V in years past, but I haven't seen one of those in years... pretty much AA/AAA these days. As Bill said, I've only seen 9V in clock radios for backup, nothing else.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[VEBill]

9-volt batteries are still commonly used in the transmitters (and receivers) for inexpensive RC toy cars, etc.

If there is a world-wide ban on designing 9-volt batteries into anything other than smoke detectors, then I didn't get the memo... ;-)

 

[MacGyverS2000]

Ah, yes... Radio Shack is the world dominator for selling Taiwan-made RC toys that use 9V in the pistol grip-style transmitters.


Dan - Owner

http://www.Hi-TecDesigns.com

 

[LionelHutz]

I would imagine the move to AAA batteries in things like remote controls has more to do with the low voltage components available today then the requirement not to use 9V batteries.

 

[bogeyman]

My Fluke DVMs all use 9v batteries and my smoke alarms have a linked system which powers them from the alarm box.

 

[Skogsgurra]

Re. move to AAA. Remotes with space for a 9 V battery wouldn't be accepted today. AAA is a lot easier to fit in a thin unit.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[jimkirk]

Check out

http://www.batteryuniversity.com

for lots of good information about batteries of all types.

If you go the AA or AAA route, it is best to have all the same type cell and all the same age/usage pattern.
Get all new cells and once you've assembled them into a battery pack, keep them together. Don't mix old with new.

I'd avoid Nickel-Cadmium (NiCad) batteries. Cadmium is nasty stuff. Restricted in RoHS compliant countries. Go with nickel metal hydride (NiMH). They are less tolerant of over-charging than NiCad, but are environmentally much better. You need a charger specifically designed to handle NiMH. (It will also be able to charge NiCads if you must, but a NiCad charger can't necessarily charge NiMH safely, and may easily damage the battery or reduce their useful life.)

Also, dispose of your old batteries properly. Recycle them. Depending on where you are there may be businesses and organizations that will handle this. Nickel is a valuable commodity these days and quite recycleable. If you've got old NiCad batteries, cadmium is very bad for the environment. Don't just dump them in the trash.

 

[tinfoil]

Re 9V for remotes:

It is much cheaper nowadays to build remotes that run on 2.8V than 9V (or whatever the '9V' batteries actually deliver at the end of life), so they use 2x1.5v batteries.

The world is always built the 'cheapest' way, when it comes to consumer products - therefore AA batteries replaced 9V units.

It has nothing to do with 'code' requirements - do you really think that Korean or Japanese electronic mfrs care what building codes are enacted in Wyoming or Pittsburg?

 

[MacGyverS2000]

It has nothing to do with 'code' requirements - do you really think that Korean or Japanese electronic mfrs care what building codes are enacted in Wyoming or Pittsburg?

They would if the majority of their product's market share was in the US.

Dan - Owner

http://www.Hi-TecDesigns.com