![]() ![]() ![]() The table below shows the temperature compensation at this rate for a 12V AGM battery and the temperature-compensated AGM absorption and float voltages for the whole charging temperature range. I was not able to find a rate for UPG.Ī default temperature correction of -25 mV/☌ or -14 mV/☏ should be OK for all AGM batteries both for the absorption and float voltages, unless more specific information is available. for absorption voltage, I assume) and -20 mV/✬ for “standby use” (i.e. Mastervolt specifies a higher rate of -30 mV/✬ or -17 mV/✯, while Mighty Max gives two temperature compensations: -30 mV/✬ for “cycle use” (i.e. For the common six-cell 12V battery, this translates to -23 mV/☌ or -13 mV/☏. Ī typical value for AGM battery temperature compensation is -3.9 mV/☌ or -2.2 mV/☏ per cell. This adjustment is called temperature compensation. These voltages are usually given for +25☌ or +77☏, and should be adjusted if the battery is warmer or colder. The optimal absorption and float voltages for AGM batteries vary with battery temperature. ![]() The manufacturer recommended, temperature-compensated float voltage should be the best compromise when in doubt, prefer a lower voltage. ![]() The value of the float voltage is actually a compromise between ensuring full charge and avoiding overcharging: a high float voltage value keeps the battery at 100% with certainty, but risks overcharging in long storage periods a low float voltage is safe, but may not keep the battery full and in the best of conditions. Note that the optimal float voltages depend on temperature and should be corrected with the same temperature compensation factor as the absorption voltages. If you cannot find a recommendation for your AGM battery brand, a default float voltage of 13.5V at +25☌ (+77☏) is probably a good choice. The table below summarizes the float voltage ranges for 12V and 24V batteries. Mastervolt gives a single value of 13.8V, while Mighty Max, UPG and Victron give ranges of 13.2V to 13.8V, 13.6V to 13.8V and 13.5V to 13.8V, respectively. Its purpose is to compensate for self-discharge and keep the battery fully charged and in good condition the float voltage this is the conventionally recommended storage voltage of the battery.įloat voltages specified for 12V AGM batteries are between 13.2V and 13.8V, and vary slightly with the manufacturer. Note that the optimal absorption voltage of AGM batteries depends on temperature – see temperature compensation below.įloat voltage is the charging voltage for the last “float” stage of AGM battery charging. If your AGM brand is not listed, a default absorption voltage of 14.5V at +25☌ (+77☏) is probably a good choice. I recommend you use the middle of these ranges as a starting point. Victron specifies two ranges: 14.2V…14.6V for a “normal” charging cycle, and 14.6V…14.9V for fast. As an Amazon Associate we earn from qualifying purchases.)įor 12V standard batteries, Mastervolt specifies a single voltage of 14.25V, while Mighty Max and UPG give a ranges of 14.4V to 14.7V and 14.6V to 14.8V, respectively. For reference, the table also includes the absorption voltages I measured from two chargers in AGM mode and links to the chargers in Amazon. Battery manufacturers give slightly different absorption voltages (or voltage ranges) for their AGM units, as listed in the table below. The optimal absorption voltages for AGM batteries are between 14.2V and 14.9V. It is often somewhat misleadingly quoted just as “charging voltage” – the bulk stage, which is most of the charging, actually happens at a much lower voltage. Absorption voltage is the full charging voltage that the charger reaches at the end of the bulk charge stage and sustains through the absorption stage. ![]()
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