Battery. Dual. Pros and cons. I have both.

[Rocket Surgeon]

I don't see this well wrote out anywhere else. Allow me to ask and explain:

I have two K2500's, a 97 and a 98, 5.7, each with NV4500.

Both were factory original dual battery equipped, but the 98 had the secondary driver's side battery removed and all cables cut out. It appears that there the secondary battery solenoid remains intact on the 98.


1 How important is it to have duals?

2 Is there a risk to having batteries of different health?

3 If one battery goes bad does it risk damaging the secondary battery?

4 What is the secondary solenoid for?

5 Does it serve to isolate and protect the battery?

6 Any thing I have not thought of that would be good to know?



If the battery is weak, you can push start (laughs, with what?) the nv4500, I presume.

 

[Orpedcrow]

2 Is there a risk to having batteries of different health?

Yes, in a short explanation the stronger one will try to charge the weaker one and they end up killing each other.

I always buy both batteries at the same time and make sure they have the same date codes.

I don’t know how the factory wires them but in a perfect world you’d want an isolator between them to help prevent homicidal batteries.

 

[Orpedcrow]

Technically the only purpose of a battery is to provide power to the starter. Then the alternator takes over to provide power to the rest of the vehicle.

But, the do act as a buffer for high loads (think about a worst case scenario, running everything at once. Highbeams, defrost, blower on hi, radio blasting, wipers, brake lights, dome lights etc… plus if you add on aftermarket stuff, lights, winch etc… it becomes a bigger demand than the alternator can put out.)

 

[1998_K1500_Sub]

act as a buffer for high loads

^^^ this

Think “snow plow”.

Winches and tailgate bulk material spreaders too, perhaps.

I suspect there are others, I’m just grasping.

 

[packer0440]

Like said above, they are good for running high electrical loads, i.e. plows, winches, camper accessories (hence why it is included with the camper special package). They don’t provide additional starting power due to the isolator. When truck is off, the 2nd battery does not power anything, and is disconnected from the primary battery (“protects” it from bad battery)

 

[1998_K1500_Sub]

camper accessories (hence why it is included with the camper special package). They don’t provide additional starting power due to the isolator.

This ^^^

Some people will use the isolated second battery to power "hotel" loads while the engine's off, e.g., 12V camper lighting and such (in which case one might consider using a deep-cycle 2nd battery... it's not something I've really thought about until now).

It's not clear to me that the isolator "relay" was OE on dual-battery systems, maybe it's a common modification.

See the attached single and dual battery wiring diagrams from the 1998 service manual. I assume other years are similar. Comments are invited.

Didn't all Diesels get the dual battery option?

 

[packer0440]

This ^^^

Some people will use the isolated second battery to power "hotel" loads while the engine's off, e.g., 12V camper lighting and such (in which case one might consider using a deep-cycle 2nd battery... it's not something I've really thought about until now).

It's not clear to me that the isolator "relay" was OE on dual-battery systems, maybe it's a common modification.

See the attached single and dual battery wiring diagrams from the 1998 service manual. Comments are invited.

I assume all Diesels got the dual battery option on account of starting load (yes?).

Diesel 2nd batteries and auxiliary battery option are different. The second battery on a diesel actually helps start the engine. The auxiliary one does not. My 1992 with the camper special package has this; the relay is indeed factory. Disconnecting it has no effect on starting. Diesel engines will actually have the batteries connected in parallel, while the auxiliary option just goes to the power block through the relay, switched off normally. I will add that I’m not as familiar with later models; they could have changed it up at some point

 

[1998_K1500_Sub]

Diesel 2nd batteries and auxiliary battery option are different. The second battery on a diesel actually helps start the engine. The auxiliary one does not. My 1992 with the camper special package has this; the relay is indeed factory. Disconnecting it has no effect on starting. Diesel engines will actually have the batteries connected in parallel, while the auxiliary option just goes to the power block through the relay, switched off normally. I will add that I’m not as familiar with later models; they could have changed it up at some point

Everything you've said makes complete sense, I just don't see it in the 1998 wiring diagrams. As you said, there may have been changes made through the years.

Honestly, the wiring diagram I posted (from the 1998 FSM) doesn't make sense for the Diesel or any situation where the LH (2nd) battery is required to supply starting current. In the diagram, the LH battery is shown wired via the stud on the underhood / firewall fuse, which connects it to the RH (main) battery (and then starter) via that LONG (8ga?) wire that snakes over the radiator shroud.

Maybe the diagram I posted is just wrong. Well anyway, it provides perspective.

 

[L31MaxExpress]

I put the auxiliary battery in my 97 Express It too used an isolater relay. The relay IIRC is 250a and it ties the batteries together in Run or Start key position. Its main purpose is a house battery though.

 

[1998_K1500_Sub]

I put the auxiliary battery in my 97 Express It too used an isolater relay. The relay IIRC is 250a and it ties the batteries together in Run or Start key position. Its main purpose is a house battery though.

I actually have something similar on my 1998 Suburban. It was single-battery system when new. The LH (2nd) battery tray was added, and an isolation relay connects the LH battery to the stud on the underhood / firewall fuse block ONLY when IGN in RUN.

The 2nd battery is used for house power when the engine is off.

It's also been used as a jumper battery when the main battery wasn't up to the task.