EL
BG
DE
ES
FR
ITGlossary · Batteries
Float Charging
A continuous low-level charging method to keep UPS batteries full and prolong their lifespan.
Technical level:Intermediate
Once the battery is full, the UPS charger holds a steady voltage slightly above nominal, enough to make up for self-discharge without overcharging. For a 12 V lead-acid battery this is typically 13.5–13.8 V at 20–25 °C.
The correct float voltage largely determines battery life. Too high a voltage causes drying out and swelling, while too low leaves the battery partly charged and leads to sulphation. That is why many UPS units adjust the voltage according to temperature.
Heat remains the biggest enemy: in a room constantly above 25 °C, the life of a VRLA battery drops considerably, however correct the charging. Place the UPS in a cool, well-ventilated spot.
Related terms
- Eurobat Design Life ClassesA classification of sealed lead-acid batteries by their design life on float charge at 20 °C.
- Fast ChargingA charging method that restores battery capacity quickly without damage by controlling current, voltage and temperature.
- State of Charge (SoC)A battery's current charge level as a percentage of its capacity, from 0% (empty) to 100% (fully charged).
- Battery Charging CurrentThe amount of current supplied to charge a battery, regulated by the UPS system.
- Battery Management System (BMS)A system that monitors and manages the performance, health, and charging of batteries.
- C-rateThe charge or discharge current expressed as a multiple of battery capacity, e.g. 1C for a 100 Ah battery means 100 A.