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EnergyCell Batteries
maintaining the absorption voltage). At this point the charger is allowed to exit absorption to the next stage.
Not all chargers measure their absorption stage in amperes. Many chargers maintain absorption for a timed
period (often two hours), under the assumption that the current will taper to the desired level during this time.
However, if the charger exits absorption and ends the charge before the current has tapered down to the
desired level, the battery may not reach 100% SoC. Repeated failure to perform a complete charge will result in
decreased battery life. If possible, it is recommended to use a DC ammeter to observe and time the current as it
tapers to the proper amperage. The user can then manually set the charger's absorption timer accordingly.
Float Stage
The float stage is a maintenance stage which ensures the battery remains fully charged. Left with no
maintenance, the battery will tend to slowly lose its charge. The float stage provides current to counter this
self-discharge. As with the absorption stage, float is a constant-voltage stage which supplies only enough
current to maintain the designated voltage.
The voltage requirements for float stage are much lower than for bulk and absorption. The voltages per
model of EnergyCell RE are listed in Table 6 on page 19. The float stage should provide enough current to
maintain the appropriate voltage. If batteries are in series, this number should be multiplied by the number of
batteries in the string.
Freshening Charge
A maintenance or "freshening" charge is given to batteries that have been in storage. The freshening charge
must be appropriate to the battery model. All charging should be temperature-compensated (see below).
With a three-stage charger, voltages are set as noted in Table 6 on page 19.
If a specialized VRLA charger is available, it should charge EnergyCell RE batteries at 14.4 to 14.8 Vdc
continuously for 16 hours before use.
Notes on EnergyCell RE Charging
The current requirements for the absorption and float stages are usually minimal; however, this will vary with
conditions, with battery age, and with battery bank size. (Larger banks tend to have higher exit current values
for the absorption stage, but they also have higher float current.) Any loads operated by the battery while
charging will also impact the requirements for the charger, as the charger must sustain everything.
Not all chargers exit directly to the float stage. Many will enter a quiescent or "silent" period during which the
charger is inactive. These chargers will turn on and off to provide periodic maintenance at the float level, rather
than continuous maintenance.
Constant-Float Charging
"Constant-float" charging may be used with the EnergyCell RE in backup power applications where the battery
bank is rarely discharged. When a discharge occurs, it is critical to recharge the bank as soon as possible
afterward. When charged with a constant-float charger, the charger should be set to maintain the batteries at
13.65 Vdc per battery in a string (2.30 volts per cell) at room temperature. The batteries are considered to be
fully charged when the cell voltage is maintained at this level and the charge current has dropped to a low level
over a long period of time. In constant-float charging, it is critical to compensate the settings for temperature.
The EnergyCell RE is not optimized for constant-float. OutBack recommends using the EnergyCell GH instead.
Temperature Compensation
Battery performance will change when the temperature varies above or below room temperature (77°F or 25°C).
Temperature compensation adjusts battery charging to correct for these changes.
When a battery is cooler, its internal resistance goes up and the voltage changes more quickly. This makes it
easier for the charger to reach its voltage set points. However, while accomplishing this process, it will not
deliver enough current to restore the battery to 100% SoC. As a result, the battery will tend to be undercharged.
Conversely, when a battery is warmer, its internal resistance goes down and the voltage changes more slowly.
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900-0127-01-00 Rev C
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