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Battery Discharge During Storage


Issue:

The shelf life of a UPS battery under storage conditions depends on battery ratings and ambient temperature.

Product Line:

All UPS products

Environment:

All models, All Serial Numbers

Cause:

Normal behavior.

Resolution:

The shelf life of a UPS battery under storage conditions depends on battery ratings and ambient temperature. For each APC UPS family the expected battery discharge rate is presented for various storage conditions.

Temperature Effects:

The type of battery used in all UPS products has a "self-discharge" characteristic. This is the amount of charge the battery will naturally lose even if it is disconnected. At 20° Celsius, a battery will lose 3% of its capacity per month. However, at 40° Celsius, a battery will lose 10% of its capacity per month.


For Back-UPS, Back-UPS Office, Back-UPS AVR, Back-UPS Pro, Smart-UPS v/s:

When any of these APC UPS models has been powered "off", the battery discharge is equal to the self-discharge rate.


With Smart-UPS:
There are two ways to turn off a Smart-UPS. When applicable, if the UPS is switched off by using the rear switch, then the battery discharge is equal to the self-discharge rate. However, if the UPS is switched off with the front panel button, then the self discharge rate at 20° Celsius will increase from the natural 3% to 5% per month. The lost power goes into a small micropower circuit which is needed in order for the UPS to "remember" if it is supposed to restart automatically when the AC power is restored.


With SmartUPS RT (1kva to 10kva):

Any time a SmartUPS RT (1kva to 10kva) will be turned off without input power present, or allowed to operate in bypass for over 24 hours, the battery modules should be disconnected to prevent unnecessary discharge. Depending on the health of the batteries, they can discharge below start-up voltage (approximately 85vDC) within 72 hours if the UPS is not operating normally.


With SmartUPS RT (15kva to 20kva):

Any time a SmartUPS RT (15kva to 20kva) will be turned off without input power present, the battery modules should be disconnected to prevent unnecessary discharge. However, unlike the smaller RT units, the 15kva and 20kva SmartUPS RT's are able to charge batteries while in bypass mode.


With Matrix-UPS:

There are two ways to turn off a Matrix-UPS. If the UPS is switched off using the rear switch, then the battery discharge rate is slightly higher than the natural self-discharge rate, which is 5% at 20° Celsius. The extra power goes into "bleeder" circuits which are required to discharge the large capacitors inside the unit in order to protect service personnel.

However, if the UPS is switched off with the front touch switch, then the self discharge rate at 20° Celsius will increase from the natural 5% to 7% per month. The additional lost power goes into a small micropower circuit which is needed for the UPS to "remember" if it is supposed to restart automatically when the AC power is restored.

If a Matrix-UPS is to be stored in this condition (i.e. off) for a long period of time, it is recommended that the batteries be detached from the Matrix-UPS Electronics Unit, as this will reduce the self-discharge rate to 3% per month.


With Symmetra, Symmetra RM and Symmetra LX:

Any time a Symmetra will be turned off or allowed to operate in bypass for over 24 hours, the battery modules should be disconnected/disabled to prevent unnecessary discharge. Depending on the Symmetra model in use, batteries can discharge below start-up voltage (approximately 90vDC) within 72 hours if the UPS is not operating normally.


Bottom Line:

APC Batteries should be charged to 100% within 6 months of purchase by the end user. If the batteries are to be stored for an extended period of time after that, the following procedures are strongly recommended in order to keep the batteries from discharging beyond the safe limit:
 

  • If the ambient temperature during storage is - 15°C to + 30°C (+ 5°F to + 86°F), perform a full recharge cycle at least every six months.
  • In environments where the ambient temperature is + 30°C to + 45°C (+ 86°F to + 113°F), perform a full recharge cycle at least every three months.
     
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