Battery storage in Volts. Why?

[WonderingFar]

Please excuse the ignorance but why is battery storage capacity measured in volts and not, for example amp hours? Wouldn't knowing how many amp hours are left be much more useful? And why does a 12V battery system have an availability of 13 or more volts? 

Getting my head around solar systems and I think I get it all apart from this.

Many thanks

 

[ZoNiE]

It's a good question.

You do measure storage in Amp Hours. People tend to use a dropping voltage as a guide to diminishing storage because they have no other method of measuring it.

A 12V battery is actually 12.6V. Comprised of six 2.1V cells.

They are charged at 13.8V or higher, depending on your charge controller. The cells require 2.2-2.3 volts to accept a charge.

If you get a good charge controller (solar) like a midnight Kid or get a monitor like a Trimetric, they will give you the storage in Amp Hours.

 

[jimindenver]

This is a basic conversion for your battery at rest with no loads on it.

 

[BradKW]

Bob did a nice video on this recently, maybe someone can link it, I'm from phone for awhile.

I hesitate to say, but in my journey it did throw me for a loop, that amp hours is a storage analogy that is awesome, but only when dealing with 12v systems. Watt hours is more accurate, but likely not necessary to get your head around unless doing something outside the norm here.

 

[RossCoe]

WonderingFar- Here is the 1st part of solar made easy, then the 2nd part should follow automatically.

 

[VaBikePacker]

Learn OHMs law.....

 

[ccbreder]

A 100 amp hour rating means they tested at 5 amperes discharge for 20 hours. Lower discharge more hours, higher discharge means less hours by a special factor (Peukert's law) that means something like 10 amps for 8.5 hours, not 10. As it gets complicated we find easier means to estimate the overall charge of our batteries. The cheapest is to check the voltage after the batteries rested with 0 discharge and 0 charge for 24 hours or overnight if we are in a rush. It is just an estimate. We can check the specific gravity of the acid, again after rested. But much more accurate.