NiMH battery ratings?

[Roy Smith]

I've got so many gizmos that take AA batteries, I'm thinking of
investing in a bunch of rechargeables. In the past I've had horrible
luck with NiCD, so I'm thinking NiMH.

I'm looking at the specs for a bunch of them
(http://www.onlybatteries.com/items.asp?db=62) and see AA's rated for
anything from 1400 mAH to 2300 mAH. How is this possible? Same
chemistry, same size. I can see some small variation in capacity, but a
factor of 1.6? Do brands really differ that much in capacity, or are
the ratings just a crock?

 

[Tim Wescott]

Roy Smith wrote:

I've got so many gizmos that take AA batteries, I'm thinking of
investing in a bunch of rechargeables. In the past I've had horrible
luck with NiCD, so I'm thinking NiMH.

I'm looking at the specs for a bunch of them
(http://www.onlybatteries.com/items.asp?db=62) and see AA's rated for
anything from 1400 mAH to 2300 mAH. How is this possible? Same
chemistry, same size. I can see some small variation in capacity, but a
factor of 1.6? Do brands really differ that much in capacity, or are
the ratings just a crock?

Battery construction can significantly affect the capacity. In general
making the battery cheaper will decrease capacity, as will making it
capable of high discharge current.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

[Peter A Forbes]

On Sun, 15 Aug 2004 14:22:28 -0400, Roy Smith <roy@panix.com> wrote:

I've got so many gizmos that take AA batteries, I'm thinking of
investing in a bunch of rechargeables. In the past I've had horrible
luck with NiCD, so I'm thinking NiMH.

I'm looking at the specs for a bunch of them
(http://www.onlybatteries.com/items.asp?db=62) and see AA's rated for
anything from 1400 mAH to 2300 mAH. How is this possible? Same
chemistry, same size. I can see some small variation in capacity, but a
factor of 1.6? Do brands really differ that much in capacity, or are
the ratings just a crock?

Just as AA cells had a low and high rating, there are also the same for Nickel
metal hydride batteries.

Also note that 'some' capacities may be quoted at different discharge rates
which will throw up different capacities, and lastly also note that consumer and
industrial cells can be different again.

In the days when Nicads were popular, 'C' cells came in industrial 2AH or 2.2AH,
but consumer cells were only 1.2AH, and often consisted of an RR cell inside a C
cell casing. Same with the D cell, industrial was 4AH or 4.5AH, consumer was
2AH, C cell in a D casing.

Peter

--
Peter & Rita Forbes
diesel@easynet.co.uk
Engine pages for preservation info:
http://www.oldengine.org/members/diesel

 

[Dave VanHorn]

(http://www.onlybatteries.com/items.asp?db=62) and see AA's rated for
anything from 1400 mAH to 2300 mAH. How is this possible?

Good engineering, or good marketing BS.

Same chemistry, same size. I can see some small variation in capacity,
but a
factor of 1.6? Do brands really differ that much in capacity, or are
the ratings just a crock?

Nope, but stick with name brand cells from a reputable disti.
Sanyo "C" type NIMH cells are quite good, but about double the price of the
cheap chinese knockoffs. These cells have nearly the overcharge tolerance of
Nicads, at the expense of a little capacity. They are slightly less
amp/hours than the highest capacity sanyo cells. The knockoffs have good
capacity, but may lack proper vents, or excess plate capacity, or the
expensive catalyst for hydrogen/oxygen recombination. When that happens, a
charged cell is also an armed thermal grenade. I've seen these cells spew
boiling electrolyte strong enough to strip two layers off a 4 layer PCB in
seconds. I've seen them "go nuclear" up to 24 hours after a perfectly normal
charge. Most of them work just fine, but a few percent have problems.

 

[Spehro Pefhany]

On Sun, 15 Aug 2004 17:27:15 -0500, the renowned "Dave VanHorn"
<dvanhorn@cedar.net> wrote:

The knockoffs have good
capacity, but may lack proper vents, or excess plate capacity, or the
expensive catalyst for hydrogen/oxygen recombination.

Don't bet on anything when it comes to some of these guys.. I know a
US specialty consumer products company that had to throw away tens of
thousands of custom battery packs because they were something like
20%-25% lower mAh capacity than rated.

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

 

[Peter A Forbes]

On Wed, 13 Oct 2004 20:01:28 +0000 (UTC), munged@address.com wrote:

Peter A Forbes <diesel@easynet.co.uk> wrote:

In the days when Nicads were popular, 'C' cells came in industrial 2AH
or 2.2AH, but consumer cells were only 1.2AH, and often consisted of an
RR cell inside a C cell casing. Same with the D cell, industrial was
4AH or 4.5AH, consumer was 2AH, C cell in a D casing.

Peter

------- Original text edited to fit 80 columns -------

Right Peter - here's more battery "truth in advertising" from Tricia's
website: http://www.tactical-link.com/wierd_stuff.htm

D.

That certainly shows the truth!

There is/was a similar thing with the 6V lantern batteries, the Gates/GE
rechargeable were 2.5AH but the dry battery was much larger in capacity.

The 21.5AH battery had a resistor inside to restrict charge/discharge current.

Peter

--
Peter & Rita Forbes
Email Address:
diesel@easynet.co.uk
Web Pages for Engine Preservation:
http://www.oldengine.org/members/diesel