Section 5: Battery Characteristics and Handling
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Section 5: Battery Characteristics
and Handling
See Specifications in Section 2: Description of Charging System for battery
capacity, discharge time, and charge time.
Battery Self-Discharge
All batteries show a decline in charge over time, even when not connected to a
load. This decline is called self-discharge. NiMH batteries self-discharge up to
20% in the first 24 hours after charging, then as much as 15% per month.
• Self-discharge is highly temperature dependent. NiMH batteries self
discharge about three times faster at 40 °C than at 20 °C.
• Age also effects self discharge. Older battery packs self-discharge faster
than new ones.
To ensure maximum battery pack capacity, charge the pack no more than
12 hours before use.
Battery Charging Temperature
NiMH battery packs last longer when charged at a low temperature. Whenever
possible, charge the battery in a cool environment away from heat sources,
including sunlight.
Rapid changes in temperature may interfere with the charge cycle. An ambient
temperature change of 1 to 2 °C per minute may cause early or late termination
of the charge cycle. Moving a charging battery pack from a cold environment
to a warm environment may cause early termination of the charge cycle. If you
must move the battery while charging:
1. Write down the energy already added to the battery pack.
2. Press the Reset button to interrupt the charging cycle.
3. Press the Charge button to re-start the charging process. Add the energy
from this charging cycle to the energy noted in Step 1 to get the total
energy added to the battery pack.
Battery Conditioning and Voltage Droop
Voltage droop is a common problem in NiMH and Ni-Cad batteries. Often
inappropriately referred to as memory effect, voltage droop is a phenomenon in
which the average battery voltage during discharge decreases. This results in
decreased battery capacity. Voltage droop may be generated in several ways;
the most significant are long-term storage (30 days or more), repeated partial
discharge, and overcharging. Voltage droop can be avoided in normal
oceanographic applications by discharging partially spent battery packs
with the charger before recharging.
Battery conditioning is the process of charging and fully discharging a battery.
This is usually repeated several times to restore the full capacity of a battery
pack suffering from voltage droop. The maximum benefit of conditioning
occurs within five charge/discharge cycles. One or two cycles are usually
sufficient when a battery pack is removed from long-term storage.
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