> I try to make stuff "customer proof" where possible. It does pay off.
> Short circuit proof, reverse polarity proof and the like.

I make a communicator sold for disability use. "Caregivers" and others are
not known for their attention to battery recharging details. I have seen
some equipment with a fast charge capability of a few hours that then sits
there and boils its batteries. People often leave them plugged in overnight
or all weekend.

With my equipment there is a right way to charge it but the OK way is "plug
in a plug pack (aka wall wart) that has a plug end that will fit in the hole
and leave it overnight". The "correct" charger is 12v at well under 200 mA
but anything from about 6v to 20v odd is OK and it can be AC or either
polarity DC. Design charge time is, purposefully, "overnight" but you can
leave it plugged in as long as you wish without damage. 6v is a bit low but
will charge. Inside is a bridge rectifier and a constant current source set
to about battery 12 hour rate and a battery pack maximum voltage limit.
There is a LED charging monitor with brightness a function of connected
charger voltage. Batteries last as long as in any other gear I have seen
around. (Some have died early but many models over 5 years old still have
original batteries) Oldest of these is now about 7 years old and I imagine
some have original batteries. A better design would have a timer shut off or
monitor battery condition but it hasn't proved necessary.

        RM

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