Insulin Pump Users

On Refrigerating Batteries:

I thought that this topic has sufficient interest from this list to do some
research about what the technical literature says on the
topic. With the assistance of a physicist friend, we have determined the
following:

1. Perry’s Chemical Engineering Handbook.

There is no discussion about storage temperature, but when the go through the
thermodynamics it is clear that the voltage is
affected by temperature by virtue of the second law in which the term TdS
appears in the general energy equation. This is probably
valid during operation, and not storage.

2. Mark’s Mechanical Engineering Handbook

Discusses storage only in passing. Dry cells can be frozen, and then completely
rejuvenated upon bringing back to proper
temperature. The apparent conclusion here is that if the battery is
installed while at the low storage temperature, before it
has warmed up, then the voltage would be lower and hence might screw up the pump
control chip. If so, it would certainly be best
to allow the battery to warm up be fore installation.

But, the pump does have a low temperature performance limit (not sure what that
is). The internal circuitry must compensate for
voltage variations up to that limit, at least.

My physicist friend has often stored all types of batteries in his refrigerator,
C, D, Zn-air, 9V, 6V, etc. Also, when C or D cells
weaken he used to heat them up (not too long, or they explode messily.
However, he is not sure why he did this in the past.

3. Van Nostrand’s Scientific Encyclopedia

Contains huge chart of all battery types, and the Silver Oxide (the one the pump
uses) is touted as the one that has indefinite
shelf life, and it would be inferred that they mean at ambient temperature,
since they don’t specify explicitly.

This last is the most relevant statement found relating to the pump. One could
conclude that the Silver Oxide batteries can be
stored indefinitely, and do not need refrigeration. Also, if one chooses to
refrigerate, be sure and return them to room
temperature before using!

Perhaps there are some Electro-Chemical specialists on this list who might be
able to comment more succinctly. Also, a follow up
with MiniMed might be in order to obtain their official position regarding this
topic.

David

This entry was posted on Thursday, June 23rd, 2005 at 4:16 am and is filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.