Manual
745-680-B8-002, Rev. B
10
Fig. 1-2, Capacity Related toTemperature and Discharge Rate
1.2 Specications and General Information, continued
Gassing
SMU-F batteries have a high recombination efciency (>98%) and for cells operated at 68ºF (20ºC)
under normal operating conditions venting is virtually negligible. The following gassing rates can be
expected:
2 ml/Ah/cell/month at a oat voltage of 2.27Vpc.•
10 ml/Ah/cell/month at a recharge voltage of 2.40Vpc.•
As hydrogen should never exceed 2% by volume in any enclosed space, all rooms or cabinets where
batteries are installed should have natural ventilation and not be fully sealed.Customers should also
be aware that hydrogen is very light and can “pocket” in portions of the room or cabinet. Designers
should take this into account when designing the battery operating space.
Each cell has a one-way valve to permit the release of gases from the cell whenever the internal
pressure exceeds the xed safety value. The valve is rated at approximately 0.1 atmospheres (1.5
PSIG or 10 kPa).
Operation of batteries in parallel
When the required capacity is greater than the maximum available from our range, it is possible to
connect batteries in parallel to obtain the desired capacity.
Use only blocks of the same model•
Make all electrical connections of parallel circuits between the batteries as equal and symmetrical •
as possible (e.g., length and type of connector) to minimize possible impedance variations
Capacity
The battery capacity is rated in ampere hours (Ah) and indicates the quantity of electricity which can
be supplied during discharge. The capacity depends on the quantity of the active materials contained
in the battery (thus on dimensions and weight) as well as the discharge rate and temperature. The
higher the discharge rate, the lower the available capacity. As batteries get colder, the available
capacity is reduced. This is related to the kinetics of the electrochemical reactions and the resistivity
of the electrolyte (see Fig. 1-2).
20%
30%
40%
50%
60%
70%
80%
90%
100%
110%
Temperature ºF (ºC)
Available Capacity
1 -10 hour discharge
5 -59 minute discharge
-4 (-20) 14 (-10) 32 (0) 50 (10)
68 (20) 86 (30) 104 (40)
122 (50) 140 (60)