Dataman S4 - Manual (Page 32)

DATAMAN S4 MANUAL
32 INFO KEY
Lithium Backup Battery
Nickel Cadmium batteries lose capacity by self-
discharging at a rate of 200% per year,
according to the manufacturers. That means
that a fully-charged Nicad today will have no
charge at all in 6 month’s time.
When S4 turns itself off because the battery
voltage is low,, there is less than 1% capacity
remaining. The RAM data might only be
supported for a few days. For this reason, a
Lithium battery has been fitted to support RAM
and microprocessor data when the Nicad loses
its charge. The Lithium cell does not have this
self-discharge problem. The Lithium battery
would last over 10 years in an S4 which was
always charged, and about 2 years in one
which was always flat.
Charging from a Bench Supply.
You can also charge your S4 from a D.C.
bench supply. However this needs caution. S4
is not capable of turning off the D.C. charging
current; so this must be limited to what the
battery would take continuously without
overheating - 60ma. is safe. The D.C. positive
and negative connections can be either way
round because there is a bridge in the charging
circuit.
Avoid emulating and charging from a
bench-supply at the same time. There could
be a conflict between system grounds.