Datasheet

Rechargeable Button Cells
3.10 PERMISSIBLE TEMPERATURE RANGE
The NiMH High Rate Button Cells from VARTA Microbattery are suitable for use in a wide temperature range.
Operation Temperature During Charge
Charge efficiency is dependent on operating tempera-
ture. Due to the increasing evolution of oxygen at the
positive electrode, charge efficiency decreases at higher
temperatures. At low temperatures charge effi-
ciency is excellent due to higher charge voltage. As the
oxygen recombination process is slowed down at low
temperature, a certain rise in internal cell pressure may
occur depending on charge rate. The ranges of oper-
ation temperatures in Fig. 37 are permitted.
Operation Temperature During Discharge
Maximum capacity is obtained at an ambient tempera-
ture of about +24°C. There is a slight decrease of
capacity at higher and lower temperatures especially
at a longer period of time. This reduction in capacity
is more pronounced at low temperatures and high dis-
charge rates.
Charge Retention (Self-discharge)
Due to the self-discharge of the cells the stored capacity
decreases over time. The self-discharge is dependent
on temperature. The higher the temperature, the greater
the self-discharge over time. Losses in capacity due to
self-discharge are reversible within storage of ≤12 months
within normal ambient conditions. After long-term storage
up to three full cycles may be necessary to obtain full
capacity.
In any case, please refer also to p. 42/43, 4.3 Proper
use and Handling.
Series HR/HRT
AVAILABLE CAPACITY % of N.C.
FIG. 38
Self-discharge characteristics at different
temperatures of V...H(T) robust family
FIG. 39
Self-discharge characteristics at different
temperatures of V...HR(T) powerful family
-20°C
to
+65°C
resp.
+85°C
-40°C
to
+65°C
resp.
+85°C
0°C
to
+65°C
resp.
+85°C
FIG. 37
Permissible temperature range for
NiMH High Rate Button Cells (+65°C resp.
+85°C, depending on type. See also p. 27)
AVAILABLE CAPACITY % of N.C.
FIG. 38
FIG. 39