7
This allows us the following calculation to determine both battery life (endurance in the field) and
the time to fill the logging memory:
A
VERAGE
D
RAW
(mA)
=
0.7
(
T
‐
2.5)
+
1,000
T
Where
T
=
the
measurement
interval
in
seconds.
The
.7
(T
‐
2.5)
gives
us
the
current
total
current
draw
for
one
cycle
of
standby
because
we
draw
.7
mA
for
the
entire
interval
except
the
2.5
seconds
of
actual
measurement.
Then
we
add
the
measurement
cycle
during
draw
of
~400
mA
for
2.5s
(2.5
*
400
=
1,000).
And
finally
we
divide
by
T
to
get
the
overall
average
draw.
For
example,
the
average
draw
for
a
30
second
interval:
A
VERAGE
D
RAW
(mA)
=
0.7
(30
‐
2.5)
+
1,000
=
33.9
mA
30
To get the Estimated Battery Life (EBL), we divide the battery capacity by the average draw. In the
case of a 2,200mA battery, this would be:
E
STIMATED
B
ATTERY
L
IFE
=
2,200
/
33.9
=
64.9
HOURS
To determine the Time to Fill Memory (TTFM), we use a different calculation:
TTFM
=
SAMPLING
INTERVAL
*
5,400
DATA
LOGS
/
3,600
For example, taking a sample every 30 seconds would mean:
TTFM
=
32
*
5,400
/
3,600
TTFM
=
48
HOURS
Of course, TTFM must be less than EBL. This means that in most cases, you can completely fill the
memory with data logs more than once between charges.
Battery
Life
Data loggers using AA dry cell alkaline batteries can run continuously for up to 8 hours, regardless
of logging interval selected.
The battery life for data loggers using a rechargeable Li‐Ion battery depends on the selected logging
interval. Table below shows the estimated battery life (EBL) and the time to fill the internal
memory (TTF) based on some typical logging intervals.
Logging
Interval
(T)
Avg.
Draw*
(D)
Estimated
Battery
Life*
(EBL)
Time
to
Fill
Memory*
(TTF)
2,200mAh 6,000mAh
30 sec. 33.9 mA
65 hrs.
177 hrs.
45 hrs.
60 sec. 17.3 mA
127 hrs.
347 hrs.
90 hrs.
