What is the right battery level?

[Maggie Flinn]

How do I know how to keep my batteries at a healthy level? I have 2 6 volt Duracell 135 ah golf carts in series. 2 renogy 100 watt panels hooked to a PWM. Am in the desert in Ehrenberg and am afraid to use my 1500 watt PSW inverter because it drops down the reading by .5 volts right off the bat. I’ve seen it go all the way up past 14 volts during the day but normally is around the high to medium 12s. What is the number where I should shut it down?


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[MrAlvinDude]

The voltage reading on lead acid batteries will flux when they are being used or being charged. It has got something to do with their internal resistance. In general terms one could also say, that the internal (chemical) processes of the battery, that allows flow of energy, is reluctant or slow.

So it is completely normal for the voltage reading to drop some, when ever you start using power from the battery. 
If you observe the voltage reading for a minut or so, after you stop drawing power from the battery, you will see the voltage go up a little. And you are likely to see this happening even at night. 
In the day time, the change upwards might be a bit higher, and be a bit faster, because the change is from drawing power to being charged. 
At night the change is only between  drawing power and resting. 

If you, a couple of times every week, get readings above or close to 13.8 then you are giving your batteries a fully charge treat, that will help them live longer lives. 
The voltage should however not go too far over 14V 


Then is the big question; 'at what voltage reading should I stop drawing power from my batteries'.


In this video, a few numbers are mentioned


But I am sure others will also be able to elaborate on why it is useful to stay around or above the numbers mentioned in this video.

 

[John61CT]

> How do I know how to keep my batteries at a healthy level?

You can't rely on volts for accuracy.

First off, make sure you are getting them to 100% Full as often as you can, minimum few times a week.

Do that by watching amps decline at Absorb voltage toward the end, make sure your charge source does not go to Float until current is below 1A, or holds around that level without changing for well over an hour.


For ending discharging, get a good quality SoC meter. Best is SmartGauge, or at least some type of shunt-based AH counting Battery Monitor.

For SG stop and recharge when it says 50%.

With the latter type, when it says you've used 65AH.

As your batt capacity declines, change that to 60, then 55, etc, only a rough estimate, why SG is easier to use.

 

[MrAlvinDude]

So Maggie Flinn, did you get that?

That watching only battery voltages, are not the best way to actually know how your batteries are doing. Watching battery voltages, can only be used as a general guideline.

One reason is, that the voltage readings are not only saying something about the state of the batteries, the voltage reading is also being influenced by other factors, so only when a battery is disconnected from charging sources and usage appliances, and have been disconnected for some time, can one get a better indication of how the battery is doing by only reading the voltage.  And even then it does not give a very precise or full picture.

So using only voltage readings as the guide might end up costing your batteries a fair percentage of their potential lifespan.

The better way to go, is to use a Battery Monitor, that can express the state of the battery as a percentage of capacity. 
And the only way to even do that the propper way, is if a shunt amp sensor is added, and the battery is monitored over time, and the Battery Monitor collects data from several cycles of charge and discharge.  And not all devices that call themselves Battery Monitors does this. 



If all you have right now is however a voltmeter, then that is what you need to rely on. And then the general rule of thumb is to not go much under 12.2V. 

But please understand that any advice using only voltage readings, is not the best advice you can get, and not the best way for you to know how well you are treating your batteries. 

The best way is to use a decent Battery Monitor device, that uses a shunt sensor, so actual usage and charge data can be collected, and processed, and can be translated into an actual percentage of charge. 

And then you should never go under a 50% level of charge on those otherwise fine lead acid batteries of yours.