Fiction
While one of the major advantages of lithium batteries is that they can be discharged to near empty, many say completely empty (0% SOC – State of Charge), this is not true regarding lead acid batteries. Discharging a deep-cycle lead acid battery below half its rated capacity (50% SOC) will damage the battery, reducing its storage capacity and shortening its life span. No lead acid battery is designed to be repeatedly discharged until almost empty.
Battery experts recommend never discharging a lead acid battery below 50% SOC.
Let’s look at what they have to say:
Electricity expert Mike Sokol had this to say when writing for RVtravel.com:
“Finally, on that power question, note that modern lithium batteries can be discharged down to 0% of capacity (flat-lined) without damage, so 100-amp-hrs of lithium battery is good for around 1,2000 watt-hrs of power. That’s because 100 amps x 12 volts x 1 (full discharge) = 1,200 watt-hrs. However, a standard flooded-cell battery should only be discharged down to the 50% level or you’ll kill it rather quickly.”
The experts at Battle Born Batteries have this to say:
“What Damages Lead-Acid Batteries?
Unfortunately, many things can cause lead-acid battery damage. Because these batteries run on chemical reactions, when conditions are not right for the reaction to occur, the batteries can become permanently damaged.
For example, discharging lead-acid batteries below 50% charge will increase a chemical reaction called sulfation and damage the battery. Because of this, the battery really should never put out more than half of its rated capacity, or life will be reduced.”
Battery Zone website offers this advice:
“BATTERY TIP 4 – Never fully discharge a deep cycle lead acid battery!
The deeper you discharge the battery the more it will reduce the battery’s total cycle life. We recommend discharging a battery to no lower than 50% DOD [depth of discharge], with a maximum of 80%. If you discharge the battery to 50% of its capacity instead of 100%, the battery will produce an extra 40% more amperes over the life of the battery.”
How to know the SOC (state of charge) of a lead acid battery
The chart below can be used to determine the SOC (state of charge) for your lead acid battery. With the use of a volt-ohm meter connected to your house batteries, you will know it is time for a recharge as the voltage drops to near 12.06 volts.
Hopefully, this installment of Fact or Fiction reinforces the importance of never discharging a lead acid battery below 50% SOC (State of Charge), let alone to “almost empty”. As lead acid deep-cycle batteries aren’t cheap, I am sure everyone wants to maximize the life of their house batteries.
Test your knowledge some more with these previous Fact or Fiction questions:
- A propane furnace emits lots of moisture
- Your RV’s tank covers should never be removed
- If you see these on your RV, do not use it in winter!
- Outside temperatures can be too cold for an RV refrigerator to cool
- Never plug in with a 20-amp extension cord
- Doing THIS is the number one cause of RV fires on highways
- Propane gas has no odor
- New RV refrigerators are not designed to operate on propane above 5,500 ft altitude.
- RV tires tend to lose pressure at high altitudes
- Liquid propane expands 270 times when released into the atmosphere
##RVT1127
So all we need is a device to disconnect the lead acid battery pack at 12.06 volts. lol.
Thank you, Dave! The discussion is good, but the chart is exceptional. I have never seen the percentages associated with different charge levels. I will refine my power management system settings to activate the generator sooner when we are running on batteries. Thanks again!
Appreciate the chart but how about one for us that have 6 volts in series?
The same voltage applies. If you want to check each battery separately, the open circuit (no load) 50% SOC voltage is exactly 6.0 volts. Each one can be checked and charged individually but they should always both be fully charged before being used.
Just use 1/2 the12v measurement. The 12v readings are actually the sum of the cells and 12v batteries have 6 cells. 6v batteries have 3 cells or 1/2 the 12v voltages
Thomas,
You find a chart for 6-volt batteries here
We just learned this the hard way. A month or so ago our batteries got discharged (not intentionally) to 22%. We just got back from a boondocking trip and the batteries would not recharge above 85% even after hours on the generator. Previously, if it was sunny, the solar panel had no problem keeping the batteries charged up enough to keep up with the 12V fridge & we never had to use the generator. The batteries now will barely charge on the solar panel even though we had blazing sun all day. Now it looks like we have to replace the batteries.
For how long were they at that state of charge?
Sulfation is a process which takes time. Can anyone shed light on how long a battery can be discharged to 11.8V before irreversible sulfation will occur? Not looking for a exact answer but is it hours, days, or months?
From what I have researched, sulfur attaches to the plates as the fla (flooded lead acid) is discharged. It takes a multi-stage charger with a high voltage initial bulk or desalination charge to break up the sulfation, then does an equalization and float charge. A typical charger simply does a 13.6v charge until the battery reaches 12.6v then drops to 13.2v. This does not break up sulfation and it get thicker at each cycle diminishing the batteries ability to store power or ah.