[Tfug] OT: Batteries

[Bexley Hall]

Hi,

I'm trying to come to grips with two very different
approaches to battery selection for a device I am
designing (there are actually three but the second
is *effectively* the same as the third).

1. Customer replaceable (!) off-the-shelf batteries.
This limits the design to battery form factors,
chemistries and capacities that are "readily available"
(i.e., buy replacements at Target, etc.).  Note that
a separate issue is rechargability (as that complicates
design, adds to cost, reliability impact, etc.).  With
COTS batteries, recharging is just a *convenience* issue.

2. Proprietary battery.  This affords greater flexibility
in form factor, choice of chemistries, battery capacity,
etc.  It, however, *requires* the battery to be rechargeable
(or have a VERY long life -- years!) as replacement would
be inconvenient (and possibly expensive since that means
stocking a supply of replacement batteries and allowing
people to purchase them -- adds overhead to each such sale).

3. Proprietary battery *sealed* within the device!  (i.e.,
option 2 might be something like a cell phone approach in
which the battery *is* proprietary but the user *could*
remove/replace it if he was able to get a replacement part).
This places even more demands on the battery (from the
user's perspective) as replacing it would be a "factory
service" operation.

However, it offers some benefits that can be real wins:
- device can be made far more weather resistant (I've known
  of two cell phones "destroyed" because they "fell" into
  a toilet -- I have no idea *how* but...  :> )
- cost of manufacturing goes down as you simplify the
  design of the case
- cost of *tooling* goes down (since the case has fewer
  pieces, molds become simpler and fewer)
- no need to stock batteries or battery covers as
  replacement parts

Price point seems to play a big part in my initial
thinking on this.  E.g., a $20 device with a battery
that will last a year you can think of the battery
*and* device as "disposable" (in today's market).

OTOH, how happy would you be about discarding your
laptop/netbook after a year?  (and those aren't
actually terribly expensive!)

Comments?
--don