When not in use, it is normal to expect 10-12% self-discharge per month at 25ºC (77ºF) for Flooded models. This rate slows as ambient temperatures decrease and increase at higher temperatures. Stored Flooded batteries should be recharged every 3 months until the battery is put in service to avoid sulfation buildup and possible freezing in cold temperatures.
Rolls Flooded models with Advanced NAM carbon additive may see an increased self-discharge rate of 20-25% per month at 25ºC (77ºF) when not in use. A refresher charge may be necessary every 2-3 months.
Prior to placing Flooded batteries into winter storage, charge to 100% SOC and make certain the liquid level is approximately 13 mm (1/2”) above the top of the separators. Electrolyte in a very cold battery will be lower than normal. Allow the battery to warm to a normal ambient temperature before judging electrolyte levels. Self-discharge rate will vary by ambient temperature. Apply a refresher charge as necessary when stored for extended periods.
Example: Electrolyte may freeze if the batteries become discharged to approximately 50% SOC at -20ºC (-4ºF).
FLOAT CHARGE OR DISCONNECT?
Now the choice is whether to leave the batteries connected to your charging system or remove and store in a cool dry area. In marine applications, if the batteries are stored aboard a boat, charge completely and disconnect the terminal cables. This will prevent premature discharge of the batteries due to a ground in the electrical circuits or failure to turn a piece of electrical equipment off.
If a battery becomes discharged to 50% SOC, the electrolyte may freeze when temperatures drop to -20ºC (-4ºF) or below.
Temperatures at which electrolyte, in various states of charge, starts to freeze.
(cor. to 80° F/26° C)
|1.280||-92° F (-69° C)|
|1.265||-72.3° F (-57.4° C)|
|1.250||-62° F (-52.2° C)|
|1.200||-16° F (-26.7° C)|
|1.150||+5° F (-15° C)|
|1.100||+19° F (-7.2° C|