Re: Carving 6 volt battery

Posted by Owen_Dyneto On 2013/1/22 23:13:40

For a lead acid battery with removeable caps on the cells the most accurate way to determine the state of charge is by the specific gravity of the electrolyte (sulfuric acid and water mix, nominally about 20%). Specific gravity is measured with a battery hydrometer. A fully charged cell of a lead/acid battery should have a specific gravity of 1.275 - 1.280. 1.220 - 1.225 is about half-charge and anything less than 1.175 might make a bulb glow but indicates an essentially dead battery.

Check each cell individually of course; if the specific gravity of one does not increase while the others do while charging, that cell is "dead" and the battery is kaput. Further charging will not increase this value above 1.280. Capacity (not voltage) of a lead/acid battery drops dramatically with very low temperatures and I wouldn't leave it outdoors, either just sitting or charging. I'd guess that at 20 degrees or so, if fully charged, it should still be able to start a car or crank for a short time but there won't be much reserve capacity.

My ancient Allstate charger has a meter to indicate the charging rate in amperes; it goes to a max of 10 (depending on the state of charge of the battery) and automatically tapers to near-zero as the battery reaches full charge. If the charge rate does not eventually taper off towards zero, the battery is not capable of holding a full charge.