UPS Battery (VRLA) Life Estimator

At the datasheet rating point, VRLA/AGM lead-acid cells of this class are typically rated around the default shown (to 80% remaining capacity). Cycle at a shallower depth of discharge and the count rises steeply — that is the (DoD_rated/DoD)^k term. Heat, fast charging and storage at full charge all shorten it.

Float ageing: grid corrosion and dry-out proceed continuously at float voltage, accelerated exponentially by temperature. A VRLA in a 30+ °C closet ages at twice the datasheet rate with zero discharges. Check the room temperature, verify float voltage is temperature-compensated per the maker's mV/°C figure, and impedance-test yearly — replace on impedance rise (≥30–50% over baseline), not on the calendar alone.

Count equivalent full cycles: two 50% discharges ≈ one full cycle of energy throughput. If your charger or BMS reports total Ah or kWh throughput, divide by the pack's rated capacity to get equivalent full cycles — that is the number to enter as cycles completed.

Industry convention is 80% of original capacity — beyond that, fade accelerates and runtime becomes unpredictable. Fleets usually retire packs at 80% for the duty they were bought for, then cascade them to lighter duty rather than scrapping immediately.

Yes — it is the single biggest lever you control. Lead-acid cycled to 50% instead of 80% roughly doubles cycle count; lithium chemistries gain similarly with the exponent k shown in the formula. Sizing a pack so daily use is a shallower fraction of capacity is usually cheaper than replacing packs early.