understanding batteries

[Jc12]

Hey guys, i have a basic understanding of our 12v batteries and just recently installed a dual system. What i am now wondering is how much use i can truly get out of my secondary battery/batteries. I have a set of 20 watt led's and a 200 watt speaker which i like to bring with me camping. Both run off of 12volt batteries. My deep cycle is rated at 75 amp hours.. now i understand you can still power accessories with less than 12 volts so what exactly does the 75 amp hours mean? Say i want to use my LEDs.. if they draw roughly 2 amps i should be able to run them for 37.5 hours (theoretically). now what happens after you have reached your 75 amp hours? will the battery still be able to power anything? I wouldn't require it to start my vehicle, just power accessories. Same goes for the speaker - if it draws 16.6 amps could i really only run it for around 4-5hours then the battery is so dead it wont power anything? I suppose certain 12v accessories can still run off a battery putting out less than 12v? I guess one thing that confused me was when i pulled my key fob's battery today which is meant to be a 12v it tested at 6.7 volts yet still powered my key fob so i am trying to understand when a battery is actually dead. Thanks for any help guys

 

[IBallEngineer]

Hey guys, i have a basic understanding of our 12v batteries and just recently installed a dual system. What i am now wondering is how much use i can truly get out of my secondary battery/batteries. I have a set of 20 watt led's and a 200 watt speaker which i like to bring with me camping. Both run off of 12volt batteries. My deep cycle is rated at 75 amp hours.. now i understand you can still power accessories with less than 12 volts so what exactly does the 75 amp hours mean? Say i want to use my LEDs.. if they draw roughly 2 amps i should be able to run them for 37.5 hours (theoretically). now what happens after you have reached your 75 amp hours? will the battery still be able to power anything? I wouldn't require it to start my vehicle, just power accessories. Same goes for the speaker - if it draws 16.6 amps could i really only run it for around 4-5hours then the battery is so dead it wont power anything? I suppose certain 12v accessories can still run off a battery putting out less than 12v? I guess one thing that confused me was when i pulled my key fob's battery today which is meant to be a 12v it tested at 6.7 volts yet still powered my key fob so i am trying to understand when a battery is actually dead. Thanks for any help guys

Deep cycle batteries' amp hour rating is typically at 20 hours, so a 75 amp hour rating means it will power 3.75 amps for 20 hours to be COMPLETELY discharged. You should not go below 50% discharged. That doesn't mean 0 volts, in fact 12.0 Volts is pretty much already dead. Read this link, the draw is not linear, therefore you need advanced math, using a calculator. This link explains the amp hour ratings, there are TWO for each battery.

What does ?20 Amp Hr rate? mean?

Once you know how the amp hour rating is achieved, use this calculator to figure out how much life you'll get.

BatteryStuff Tools | Determine Run Time for Specific Load Calculator

OP, read the comments for addition understanding. For example, how to figure this out if you use both batteries together. Also because you won't be drawing your battery down to 0, all numbers should be halved. Read the comments! Ask about what you don't understand, plenty of knowledgeable heads on this forum.

:couch2:

 

[Jc12]

thanks for the reply, those links were very helpful. So if my battery were to get below 12v it wouldn't be able to power anything at all? Just trying to understand how my little 12v key fob battery will still power the remote when it only has 6-7volts left.

 

[IBallEngineer]

thanks for the reply, those links were very helpful. So if my battery were to get below 12v it wouldn't be able to power anything at all? Just trying to understand how my little 12v key fob battery will still power the remote when it only has 6-7volts left.

Micro electronics are very different, they often operate on ranges from 5-14 Volts. Don't try to apply that logic to your truck.

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