Specifications

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In this case, the battery chosen was a nickel metal hydride battery. While in the
battery comparison section, it had several advantages compared to lithium ion
and even lead acid batteries, it is not necessarily the case with the charging
technology required to charge this type of battery. Indeed, nickel metal hydrides
present several unique challenges with respect to recharging. The basic principle
of charging this type of battery is by essentially passing current through the
battery. This also means that the voltage necessary to charge these batteries is
not necessarily fixed. However, many battery packs are made from several
standard cells wired in series to increase the voltage output. As such, no two
cells are exactly the same with respect to their impedances. So even with a
regulated charging circuit output, there can still be variances in charging the pack
as a whole, as the different impedances of each cell can cause certain cells to
not charge fully, or other cells to overcharge. To address these and other
challenges, several options will be investigated.
2.12.1 Eliminating the Need for a Recharging Circuit
Given the difficulties of building a custom charging circuit, one possible option
would be to create an opening in the portable unit of the housing to allow the
user to remove the battery. This way, the user could charge the battery externally
in a pre-built charger, possibly using a solution that is already available. The user
could use a 12V car charger or perhaps even a wall charger to charge their
battery. This would be similar to many digital cameras and other consumer
electronics with removable, rechargeable batteries.
However, the previous consideration of safety must be taken into account, along
with basic quality concerns such as reliability. If the battery is made removable, it
is possible that the user may inadvertently remove the battery, rendering the
device no longer portable. In addition, the battery may be mishandled or
disposed of into the environment in an inappropriate way. It also creates an
additional point of constant wear on the housing itself. It would require the
creation of robust electrodes, housing door, and materials able to withstand a
high number of duty cycles and possibly abusive battery insertion and removal. It
may also introduce the possibility of additional user error in the form of shorting
contacts or using batteries for which the unit was not designed. Not only does
this present a hazard to the user, but can also permanently damage the unit.
The other option would be to include such a battery charger with the overall kit.
However, one of the goals of this project is to reduce cost as much as possible,
especially considering the high cost of existing solutions similar to this project. An
additional, separate charger would add cost and yet another piece which could
be damaged or misplaced. As such, this option has several disadvantages which
need to be considered carefully.