VRLA — the workhorse
Valve-Regulated Lead-Acid (VRLA) batteries are the standard UPS energy store. They are sealed, maintenance-free, safe for office environments and inexpensive. A typical VRLA string lasts 3–5 years in a UK server room, though design life ratings of 5 or 10 years exist. They are the default choice for most UPS up to large kVA ranges.
Lithium-ion
Lithium-ion (Li-ion) UPS batteries last 8–10 years, charge faster, weigh around a third as much and deliver more runtime in a smaller footprint. The higher upfront cost is offset by a longer life and lower replacement frequency, making them attractive for space-constrained, remote or long-life installations. Sentryum and Multi Power both offer lithium compatibility.
Supercapacitors
For loads that only need seconds of cover — bridging a generator start or riding through a momentary dip — supercapacitors offer millions of charge cycles and a 10–15 year life with no chemical degradation. Sentryum supports supercapacitor compatibility for these short-runtime, high-cycle applications.
What kills batteries
Heat is the biggest battery killer. Every 8–10°C above 20°C roughly halves VRLA life. Other killers: deep discharging, chronic undercharging, and strings left too long without testing. A maintenance contract with periodic impedance testing catches failing blocks before they take the whole string — and your protection — down. See our battery replacement service.
Frequently asked questions
How often should UPS batteries be replaced?
VRLA batteries typically need replacing every 3–5 years; lithium-ion every 8–10 years. Environmental temperature and cycling affect this significantly.
What is the difference between VRLA and lithium UPS batteries?
VRLA is cheaper and proven; lithium-ion lasts longer, weighs less, charges faster and stores more runtime in less space but costs more upfront.
Why do UPS batteries fail early?
Mostly heat. Every 8–10°C above 20°C halves VRLA life. Deep discharges, undercharging and lack of testing also contribute.
Can I replace UPS batteries myself?
Small tower UPS yes; larger systems should be replaced by an engineer with impedance testing and runtime validation to ensure the string is healthy and safe.