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Battery Testing and Maintenance for UPS and Standby Batteries

Oct 21
5 min read

Updated: Oct 22

C&D Technologies says its VRLA UPS batteries "are maintenance free with respect to the electrolyte", and still lists measurements to take at regular intervals (C&D 41-6965, p. 4). This guide pulls together what C&D and EnerSys publish about testing and maintaining UPS and standby batteries, and links to our detailed guides on each topic.

Who should do the work

  • EnerSys says only a qualified EnerSys service representative, or others who know batteries and the required precautions, should service its PowerSafe DDmP125-33 LP batteries. Its warning reads: "Lack of preventative maintenance could result in batteries exploding and emitting gasses and/or flame. An authorized, trained technician must perform annual preventative maintenance" (EnerSys DDmP125-33 LP manual, p. iii).

  • C&D says installation and servicing should be performed or supervised by qualified personnel who know lead-acid batteries and the required safety precautions. It lists insulated tools, eye protection and rubber gloves, removing metal objects such as watches and rings, and the latest NFPA 70E for arc-flash hazards (C&D 41-6965, p. 2).

What to check: C&D's periodic maintenance list

C&D 41-6965 covers its High Rate Max, Pure Lead Plus and Pure Lead Max VRLA UPS batteries. It lists these measurements (C&D 41-6965, p. 4):

Check

What C&D says

Visual inspection

Check for signs of leaking, corrosion, discoloration and installation integrity. Quarterly for all three ranges in Table 1.

Pilot unit temperature

Measure at the negative terminal on units in different locations in the string. Select 1 pilot unit for every 10 units.

System float voltage

Measure from the most positive to the most negative post. It should closely match charger settings and average 2.25 to 2.30 volts per cell.

Unit float voltage

Measure each unit. 12V units under 13.30 V (or 6V units under 6.65 V) while on charge may require additional maintenance.

System float current

Trend it over time, since increasing float current can be a sign of battery aging. Set a baseline after 3 months on float charge.

Ripple voltage and current

Excessive AC ripple can lead to rapid aging and should be monitored closely.

Ohmic measurement

Impedance, conductance, resistance or admittance, taken directly from the battery post whenever possible. Set a baseline after 3 months on float and trend each unit over time.

Connection resistance

Preferably with a DLRO meter, recording each connection. Annually for all three ranges in Table 1.

High-rate load test (optional)

May be applied to individual units with a handheld tester, for no more than 10 seconds.

Capacity (performance) test

Discharge testing to a published rate and duration "will give a true measure of the battery's state of health". Acceptance testing is typically completed within 3 months of installation.

C&D refers to its VRLA support documents and IEEE 1188 for more detail (C&D 41-6965, p. 4). Check the full table in the bulletin for the frequency of each item for your range.

Testing: ohmic readings and capacity tests

Records: what EnerSys says to log

For its DDmP125-33 LP systems, EnerSys says a complete recorded history of battery operation "is essential for obtaining satisfactory performance". It says to record the following (EnerSys DDmP125-33 LP manual, §19.3, pp. 34–35):

  1. After the initial charge, with the battery on float at the proper voltage for one week: individual cell or unit voltages, cell-to-cell connection resistance, terminal connection resistance, and the ambient temperature in the immediate battery environment.

  2. Every 12 months: the same readings. Any connection resistance more than 20% above its base value should be corrected.

  3. An extra set of readings whenever the battery gets an equalizing charge.

EnerSys calls this frequency "the absolute minimum to protect the warranty". It says the data will be required for any warranty claim, and more frequent (quarterly) readings are desirable (EnerSys DDmP125-33 LP manual, p. 35). It also says to read and record the pilot cell voltage monthly between scheduled maintenance (EnerSys DDmP125-33 LP manual, §18, p. 32).

For its PowerSafe SBS XL range, EnerSys says the user usually sets the schedule based on site criticality, location and manpower. Its suggested schedule (EnerSys SBS XL manual, §6) says:

  • Maintenance for standard VRLA batteries is typically every 6 months.

  • EnerSys says this interval can be extended for the SBS XL range, particularly early in service.

  • Increase the frequency as the battery approaches 80% of its intended service.

  • Keep a logbook of values, power outages and discharge tests.

  • Measure string voltage, individual bloc or cell voltages, and the ambient temperature.

  • Inspect for dust and for loose or corroded connections.

Cleaning: what not to use

  • EnerSys says not to use any oil, solvent, detergent, petroleum-based solvent or ammonia solution on battery containers or lids, because they cause permanent damage and invalidate the warranty (EnerSys SBS XL manual, §6, p. 3). For DDmP125-33 LP cells, it says not to clean with anything other than water or bicarbonate of soda (EnerSys DDmP125-33 LP manual, p. 40).

  • C&D says not to try to remove battery vents or add water, as this is a safety hazard and voids the warranty (C&D 41-6965, p. 2).

Temperature and ventilation

When maintenance finds a problem

Need testing, maintenance or replacement batteries?

We supply replacement UPS and standby batteries and provide service across the Southeast USA. Browse SWU UPS batteries and NPX high-rate batteries, or tell us about your system.

Request current price and availability: use the request form or email office@luxena.net.

Sources (checked 2026-10-21)

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