Float Voltage Recommendations for Battery Maintenance: Best Practices and Temperature Considerations

June 17, 2023

Float charging is a charging method that involves continuously monitoring and maintaining a predetermined battery voltage, regardless of the charging conditions. This charging technique is commonly utilized in stationary applications, emergency backup power systems, emergency lighting, and similar scenarios. High-quality AGM and GEL chargers often incorporate a floating cycle as part of their finishing charge algorithm. The appropriate float voltage setting is influenced by factors such as the frequency of battery discharge and temperature. In general, if the battery experiences frequent discharges, it is recommended to increase the recharge voltage to ensure sufficient charging time and maintain optimal battery performance. The typical float voltage range for monitoring and maintenance purposes is between 2.25 and 2.30 volts per cell at a temperature of 25°C/77°F.

AGM Charge and Float Voltage vs. Temperature

Temperature	Charge		Float		Temperature
(°F)	Standard	Maximum	Standard	Maximum	(°C)
≥ 120	13.6	13.9	12.8	13	≥ 49
110 – 120	13.8	14.1	12.9	13.2	43 – 49
100 – 110	13.9	14.2	13	13.3	38 – 43
90 – 100	14	14.3	13.1	13.4	32 – 38
80 – 90	14.1	14.4	13.2	13.5	27 – 32
70 – 80	14.3	14.6	13.4	13.7	21 – 27
60 – 80	14.45	14.75	13.55	13.85	16 – 21
50 – 60	14.6	14.9	13.7	14	10 – 16
40 – 50	14.8	15.1	13.9	14.2	4 – 10
≤ 40	15.1	15.4	14.2	14.5	≤ 4

GEL Charge and Float Voltage vs. Temperature

Temperature	Charge		Float		Temperature
°F	Standard	Maximum	Standard	Maximum	°C
≥ 120	13	13.3	12.8	13	≥ 49
110 – 120	13.2	13.5	12.9	13.2	44 – 48
100 – 109	13.3	13.6	13	13.3	38 – 43
90 – 99	13.4	13.7	13.1	13.4	32 – 37
80 – 89	13.5	13.8	13.2	13.5	27 – 31
70 – 79	13.7	14	13.4	13.7	21 – 26
60 – 69	13.85	14.15	13.55	13.85	16 – 20
50 – 59	14	14.3	13.7	14	10 – 15
40 – 39	14.2	14.5	13.9	14.2	5 – 9
≤ 39	14.5	14.8	14.2	14.5	≤ 4

Flooded Charge and Float Voltage vs. Temperature

Temperature	Charge		Float		Temperature
°F	Standard	Maximum	Standard	Maximum	°C
≥ 120	14.1	14.4	12.8	13	≥ 49
110 – 120	14.2	14.5	12.9	13.2	44 – 48
100 -109	14.25	14.55	13	13.3	38 – 43
90 – 99	14.3	14.6	13.1	13.4	32 – 37
80 – 89	14.4	14.7	13.2	13.5	27 – 31
70 – 79	14.42	14.75	13.4	13.7	21 – 26
60 – 69	14.45	14.8	13.55	13.85	16 – 20
50 – 59	14.48	14.8	13.7	14	10 – 15
40 – 39	14.5	14.8	13.9	14.2	5 – 9
≤ 39	14.55	14.85	14.2	14.5	≤ 4

For flooded batteries, the equalization voltage should generally not exceed 15.60 to 16 volts at a temperature of 25°C/77°F. It is important to adjust the charging voltage to compensate for temperatures above and below 25°C/77°F.