Guides
VRLA batteries in UPS use are replaced every four to five years on average, even though they are often sold with a 10-year design life. Heat, constant float charging, frequent discharges and poor power shorten that; a cool, steady room and good charging stretch it.
Because design life assumes laboratory conditions and UPS use is not that. Eaton's aging-UPS paper defines design life as the projected life under very limited use in pristine conditions, service life as the typical life under normal use, and a recommended replacement time with margin before failure; for VRLA those are 10, 5 and 4 years. Its battery paper confirms it in the field: in UPS applications, VRLA batteries are replaced every four to five years on average.
More than anything else you control. C&D recommends operating its VRLA batteries at 25 °C within plus or minus 5.5 °C as the best combination of performance and life; EnerSys gives 23-26 °C and states that elevated temperatures reduce operating life; Vertiv puts the VRLA ideal at 20-25 °C. A battery cabinet beside a hot UPS, or a room that drifts warm in summer, quietly takes years off every string.
Constant float charging overcharges a battery that is already full. Eaton explains that a UPS battery may sit on float for months without a discharge, so trickle-charge energy is forced into a full battery, which slowly corrodes the positive grid and shortens float life. Some UPS use charging schemes that rest the battery between charges to reduce this; whatever the scheme, the float voltage must match the battery maker's figure for the temperature, as C&D's manual sets out.
Generally, yes, at a cost. Eaton notes that sealed (VRLA) batteries tend to be less expensive but wear out sooner, while flooded (vented lead-acid) batteries need specialised installation and maintenance; its component table gives wet cells an average recommended replacement of 12 years, against 4 for VRLA. Flooded strings are found mostly in large UPS plants with dedicated battery rooms; most data-centre UPS today use VRLA or lithium-ion.
Readings, mostly. C&D's guidance on ohmic readings: a change of less than 20% over time is acceptable; more than 50% needs further attention, such as a load test. Other signs are blocks whose float voltage drifts from the rest, terminal temperatures above their neighbours, bulging or damaged jars, and a capacity test that falls short. Schneider Electric's advice for its UPS is simple: replace the battery immediately when the UPS says it is needed. How the readings are taken is in battery replacement and testing.
Often. Vertiv puts lithium-ion UPS batteries at 8 to 10 years or more, 2-3x VRLA life, and Eaton's table gives an average recommended replacement of 10 years. The trade-offs are covered in lithium-ion vs VRLA. For VRLA replacement strings, see these replacement battery strings for data-centre UPS; for battery service across Canada, UPS battery repair and replacement.
VRLA batteries in UPS use are replaced every four to five years on average, by Eaton's data. Lithium-ion lasts about two to three times longer.
About 25 °C, held steady: C&D gives 25 °C within plus or minus 5.5 °C, EnerSys 23-26 °C.
Yes. Constant float charging slowly corrodes the positive grid, so batteries age even without outages.
On a young string, sometimes. On an aged string, a new block among old ones tends to be mischarged, so the readings decide.
Sources, checked 2026-10-04:
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