batteries & high heat

[P3D Bob Wier <wier@xxxxxxxxxxxxxxxxx>]

Here's an interesting thing from the GPS usenet group (since
I run the USA GPS waypoint server). Although is specifically
addresses leaving a GPS unit on the dash of your car in full sun,
the conclusions will also apply to cameras that use similar cells.
Of course you should never to this anyway as it will seriously degrade
your film image quality, but it brings up an additional point...the
autowinder on my Pentax, for example, uses AA batteries...

               Bob Wier
         mailto:wier@xxxxxxxxxxxxxxxxx
  10:31 AM  Thursday, October 23, 1997
     Rocky Mountain College, Billings MT.
 keeper of the Photo-3d and Overland-Trails
mailing lists and the USA GPS Waypoint server 

================================================================= 
There  have  been  a number of reports  on  the  newsgroup  about 
batteries  sticking in various GPS receivers.  One company did  a 
study  on  the  problem with the following results  that  are  of 
general interest.

Joe Mehaffey
=================================================================     
         AA Alkaline Batteries at Elevated Temperature

As  a  result  of having some batteries stick in a  GPS,  it  was 
noticed  that the battery sleeve had started to separate  at  the 
seam which exposed some of the adhesive used to adhere the sleeve 
to  the battery.  This was the apparent cause for  the  difficult 
removal of the batteries from the unit.  The battery manufacturer 
was contacted and it was suggested that this kind of failure  was 
indicative of high temperature exposure.   Duracell and  Eveready 
rate their alkaline batteries to +54C (+130F). Duracell  provided 
some information regarding over temperature testing that they had 
completed on their AA batteries.

   -  High  temp. testing at +70C is conducted by Duracell  on  a 
sample  basis to verify product quality. There should be  no  ill 
effects at this temperature other than capacity degradation.

   - At approx. +75C the sleeve will begin to shrink.

   - At temperatures greater than +80C there becomes a  potential 
for  the  battery  to vent. Which could allow  small  amounts  of 
corrosive  material  to be expelled. The positive  side  is  that 
there should be no danger of the battery swelling or exploding.

Eveready would not acknowledge that they knew anything about the 
performance  of  their products over +54C  (+130F).  Even  though 
Duracell  did  provide  some  general  information  there  is  no 
guarantee  that  their  product  will  perform  consistently   at 
temperatures  in  excess  of  the  rated  specification  of  +54C 
(+130F).

We  have  conducted  some elevated  temperatures  and  found  the 
following:
     Test Units:
     
      Panasonic
      Eveready
      Duracell
     
   -  +70C no change in label appearance or swelling  of  battery 
case on  any of the test units.
     
   -  +75C slight change in sleeve on Eveready batteries  and  no 
change  on  Panasonic or Duracell. No swelling  of  battery  case 
observed.

   - +80C very noticeable change on Eveready and slight change on 
the   Duracell  with no change on the Panasonic. No  swelling  of 
battery   case.

   - +85C gap in sleeve as much as .130" exposed metal case and   
adhesive on the Eveready batteries. The condition of the
Panasonic and Duracell batteries remained the same. No swelling   
of battery cases observed.

The dwell time for each temperature was approx. 48 Hrs.

A  set  of  batteries  were removed from  a  GPS  unit  that  had 
completed environmental stress testing and it was found that  the 
battery  sleeves were showing the same kind of separation as  the 
tests run earlier had shown. The temperature profile that was run 
was -50C to +90C to -50C (= one cycle) for 12 cycles and  another 
12 cycles of -40C to +80C to -40C (= one cycle) with a dwell time 
of 10 minutes at each temperature.

The bottom line is that battery operated products may be  mounted 
on  the dash of a vehicle  where customers may leave them  in  an 
enclosed vehicle exposed to direct sunlight for extended  periods 
of  time.   In these cases,  there is potential for  problems  to 
occur  with regards to the batteries.  These batteries appear  to 
be compliant to our specification and the manufactures specifica-
tion.  However,  the temperatures that the unit may be exposed to 
in direct sunlight may substantially exceed the battery  manufac-
turer's rated maximum temperature.

Most AA battery manufacturers do not offer any extended  tempera-
ture alkaline batteries.   As far as is known,  no suppliers make 
extended temperature AA alkaline batteries at a reasonable  cost. 
There  are specialty companies that will do custom  packaging  of 
batteries however the cost is extreme.  At this point there is no 
total  solution  to the problem of operating  AA  batteries  over 
+130F.   

Users  of  any battery powered product should be aware  that  any 
equipment positioned on the dash of an automobile in the sun  can 
easily reach temperatures which CAN cause swelling and damage  to 
batteries.   Due to the non-availability of reasonably priced  AA 
batteries rated for these temperatures,   Users should be careful 
NOT  to leave their battery powered equipment in direct  sunlight 
in a closed vehicle to prevent the above described problems.
=================================================================

Thus,   it appears wise to protect your GPS from direct  sunlight 
exposure in enclosed vehicles.



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