Second Battery options and usage

[myles archambeau]

I am building an 04 ccsb Z71 for offroad and possibly overlanding. I have Rough Country front fog lights, rear back up lights, bed lights, rock lights, Ham radio and soon a winch and possibly a 12v fridge. I already built a fuse panel where most of that runs off of. I want a second battery for deep cycling while the engine is off. I plan to add said battery behind the coolant resevoir on the passenger side. I have looked into some information for it but would like to get a more "first hand" knowledge base. So here are a few of my questions/concerns.

 

-Stock battery is 34/78 sized battery, can I fit a group 31 in the space as they are larger because of the larger AH rating?

-I am looking into a possible solar power addition for charging, but that may be down the road so with cost and specific charging needs I think Lithium is out. I might be going with AGM. Does this have specific charging needs? If I link the starter battery and secondary through a Voltage Sensitive Relay (VSR) will the vehicle's alternator be sufficient or will a dedicated charger be needed? 

-Does the alternator only flow what is needed in amps? I see some set ups with an 80 amp circuit breaker to the second battery when I know the alternator can be around 120-140 amps. If this is the case I can get away with an 8 AWG wire instead of a 4 AWG? As the line traveled will be around 8ish feet.

-Should I stick with the 4 AWG wire in that it will help with the winches amp draw?

-Is the engine bay temperatures eliminate any battery types or brands that may be sensitive to heat?

-Any recommended batteries, set ups, things I may need to pay attention to or may have overlooked, any other advice?

 

Thank you for help as I know a winch will be a heavy draw and with all the add ons there will be a steady draw warranting a second battery, to not overwork or stress the starter battery.

Edited January 21, 2022 by myles archambeau
added another question

[richard wysong]

a second battery is factory installed with snow plow package and they just run a positive cable from battery to battery and add a ground wire from the auxillary battery to the block. if you are going to primarily run accessories when the truck is off you will want to add an isolator to the system so they just run off aux battery and the primary stays charged. RV stores carry them. the alternator has plenty of capacity to charge both bats and the voltage reg won't be affected. not sure how you would wire the winch if you use an isolator , you may not be able to run it off both bats without adding a switch to bypass the isolator. just add the circuit breaker to the load not the charging side of the system

[richard wysong]

also I would use batteries with identical ratings, I don't have a reason it  just seems like they will charge more equally.

[myles archambeau]

I plan to use identical batteries. I may not be able to buy at the same time, but they will be. The voltage relay breaks connection between the batteries when the starter side goes before 13.3v, but when the truck is running and producing 14.8v the relay will make connection so I can charge the secondary and also draw when I use the winch.

 

Relay I plan to use

https://www.amazon.com/dp/B00WTAFR84/?coliid=I16QUNO8T7HO2X&colid=3BDGLR9PML5OD&psc=1&ref_=lv_ov_lig_dp_it

 

Battery options at the moment

https://www.batteriesplus.com/productdetails/battery/car-and-truck/chevrolet/silverado-1500/2004/v8-5.3l-770cca-optional/sli78agmdp

 

https://www.optimabatteries.com/products/yellowtop-d34-78

 

I am open to other suggestions and ideas, like if the group 31 batteries fit, which do I use? Thank you

Edited January 21, 2022 by myles archambeau

[Sharpz]

Only suggestion is get the largest alternator you can get for your truck. 

[swathdiver]

These trucks are not designed to charge an AGM battery, sure you can use them just fine, they just will not last long as they could have.

 

Look up TP2, this is the code for a dual battery set up.  Batteries draw down separately but are charged together.  They ought to be the same.

 

@intheburbs Bill has done a detailed installation how to on other forums that you can easily find for the generation after yours and I think he also had TP2 on his old GMT800 Suburban as well.  He's a wealth of information to ask about such things.