Over the years while living “off grid” I have learned a thing or two from the advice of others. Some of it was good and some turned out to be no more than a myth. Batteries seem to have collected more than their fair share of myths. It might have something to do with the guess work in determining their state of charge (SOC) and depth of discharge of batteries (DOD). Whatever the reason, well intended advice could end up costing you a lot of money in new batteries.
MYTH: A fully charged battery has 12 volts. Most people are familiar with the 12-volt starter battery in a car. 12 volts is actually the “nominal voltage.” It is an agreed upon standard because saying 12.72 volts can become cumbersome. The truth is a 12 volt battery is made up of six 2-volt battery in series. Each 2-volt cell has an actual voltage of 2.12 when at rest and in standard testing conditions (STC). Each of these cells or batteries in series adds another 2.12 volts. 6 cells x 2.12 volts = 12.72 volt battery. A battery at rest with only 12 volts may very well be dead.
MYTH: Fully discharge the battery to avoid “memory”. Some people say that cell phone batteries need to be completely discharged, which is where I think this myth comes from. The myth says that if one were to use 50% of the capacity of the battery all the time eventually the battery will only be able to deliver 50% of its capacity and it will be difficult to access the other 50%. The myth goes on to say that if one were to completely discharge the battery and then charge it back up to 100% soc the memory would be erased and the full capacity of the battery would be usable again. Unfortunately for batteries used in renewable energy (RE) systems this would cause almost certain death to the battery. Maximum DOD depends on system application but, 50% is a good rule of thumb. There is no evidence that batteries used in RE systems develop a “memory.”
MYTH: Unused batteries last a long time. It seemingly stands to reason that if batteries were stored properly and not used they would last forever. Unfortunately, this is not the case. Batteries that are stored will slowly discharge even without a load. The rate of discharge varies depending on the environment. Batteries that spend a long time at less than 100% SOC will lose capacity. If you must store batteries for more than a few weeks, charge them all the way up, keep them in a cool dry place, and give them a trickle charge so they maintain 100% SOC.
MYTH: Adding water to a dead battery will help it come back to life. This might not be as much a myth as just something to do when the car won’t start because of a dead battery. If the battery does not work because the electrolyte was too low, then it is time to replace the battery and remember to check the fluid level more often.
MYTH: Don’t put a battery on concrete floor; put them on a wood board. In the 40’s and 50’s the cases of batteries were made out of hard rubber or even wood. These materials were porous, allowing the electrolyte to seep through and make contact with the ground, or in this case the concrete garage floor, which provided a path for the energy to drain out. Today battery cases are made of plastic, which doesn’t leak thereby eliminating this issue. As a matter of fact, in warmer climates the concrete floor is cooler than wood and can help keep the battery from getting to warm.
MYTH: Adding epsom salt (magnesium sulfate) brings dead batteries back to life. It is said that epsom salt will dissolve sulfates that develop on the plates of batteries and increase capacity. If conventional means to mitigate sulfating and loss of capacity have failed, it is unlikely that adding other elements to the chemical reaction will have any lasting positive effect. Don’t put additives in your batteries.
Those are some of the battery myths I have heard in my life. If you have heard of other myths or have received some “great advice” you would like to share, drop me a line.