What is float charging and what float voltage is recommended?

What is float charging? What float voltage is recommended?

This type of charge continually monitors and maintains a pre-set battery voltage, regardless of charge conditions. These chargers are used in stationary, emergency backup power, emergency lighting, and other similar applications. Most quality AGM and GEL chargers will have an alternative float cycle in their finishing charge algorithm. The frequency of discharge and temperature will dictate a more exact setting. For example, the more frequent the discharge, the higher the suggested recharge voltage should be to ensure that the recharge time is sufficient to maintain the battery's proper performance. The typical float voltage for monitoring and maintaining is between 2.25 and 2.30 volts per cell at 25°C/77°F.

Table 9 - AGM Charge and Float Voltage vs. Temperature

Temperature Charge Float Temperature
(°F) Standard Maximum Standard Maximum (°C)
≥ 120 13.60 13.90 12.80 13.00 ≥ 49
110 - 120 13.80 14.10 12.90 13.20 43 - 49
100 - 110 13.90 14.20 13.00 13.30 38 - 43
90 - 100 14.00 14.30 13.10 13.40 32 - 38
80 - 90 14.10 14.40 13.20 13.50 27 - 32
70 - 80 14.30 14.60 13.40 13.70 21 - 27
60 - 80 14.45 14.75 13.55 13.85 16 - 21
50 - 60 14.60 14.90 13.70 14.00 10 - 16
40 - 50 14.80 15.10 13.90 14.20 4 - 10
≤ 40 15.10 15.40 14.20 14.50 ≤ 4
Discover AGM
77°F 14.20 14.72 13.40 13.80 25°C


Table 10 - GEL Charge and Float Voltage vs. Temperature

Temperature Charge Float Temperature
°F Standard Maximum Standard Maximum °C
≥ 120 13.00 13.30 12.80 13.00 ≥ 49
110 - 120 13.20 13.50 12.90 13.20 44 - 48
100 - 109 13.30 13.60 13.00 13.30 38 - 43
90 - 99 13.40 13.70 13.10 13.40 32 - 37
80 - 89 13.50 13.80 13.20 13.50 27 - 31
70 - 79 13.70 14.00 13.40 13.70 21 - 26
60 - 69 13.85 14.15 13.55 13.85 16 - 20
50 - 59 14.00 14.30 13.70 14.00 10 - 15
40 - 39 14.20 14.50 13.90 14.20 5 - 9
≤ 39 14.50 14.80 14.20 14.50 ≤ 4
Discover GEL
77°F 14.10 14.50 13.35 13.75 25°C

Table 11 - Flooded Charge and Float Voltage vs. Temperature

Temperature Charge Float Temperature
°F Standard Maximum Standard Maximum °C
≥ 120 14.10 14.40 12.80 13.00 ≥ 49
110 - 120 14.20 14.50 12.90 13.20 44 - 48
100 -109 14.25 14.55 13.00 13.30 38 - 43
90 - 99 14.30 14.60 13.10 13.40 32 - 37
80 - 89 14.40 14.70 13.20 13.50 27 - 31
70 - 79 14.42 14.75 13.40 13.70 21 - 26
60 - 69 14.45 14.80 13.55 13.85 16 - 20
50 - 59 14.48 14.80 13.70 14.00 10 - 15
40 - 39 14.50 14.80 13.90 14.20 5 - 9
≤ 39 14.55 14.85 14.20 14.50 ≤ 4


Equalization voltage for flooded batteries should typically be maintained at a maximum of 15.60 tt 16 volts at 25°C/77°F. Make sure to correct the charging voltage to compensate for temperatures above and below 25°C/77°F.

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