Question for Sternwake

[Optimistic Paranoid]

I recently ran across the following recommendation on a web site.

On a 4x4 back country rig, they recommended replacing the regular battery with a marine/rec type, hooking the winch and all other accessories up to it as well as normal sil functions, and reserving the second battery for emergency starting only.

That got me wondering. If a battery were fully charged, never discharged, and constantly being "topped-up" by the alternator whenever the vehicle was being run, what would that do to it's expected life span? Increase or decrease it?

You seem to know more about this than anyone else I've met. Your thoughts on this, please?

Regards
John

 

[SternWake]

A battery which is never discharged and topped up regularly will last a long long time.

I had one battery which spent its first 23 months being cycled shallowly and then was moved to engine starting only duties, and my engine starts quickly. It lasted another 5+ years, and it was just a wally world battery.

It likely would still be working as a starting battery, but I knew its capacity was extremely limited at that age.

 

[akrvbob]

Batteries are defined by the number of times they can be cycled before they fail. A cycle is from full to half charge (or from 12.6 volts to 12.2 volts).

1) Starting batteries are rated at maybe 5-6 cycles and then they will fail.
2) Marine batteries are a few hundred cycles and then they will fail.
3) A true deep cycle battery can last thousands of cycles before it dies (think of golf cart batteries that are designed to be cycled every day).

If you never leave your lights on and run the battery down even a cheap starting battery can last 5-7 years. But leave the lights on so it won't start the next day and it will die after 5-6 times of doing that.

I replaced the starting battery in my van with a marine battery for that reason. It starts just fine and I don't have to worry about killing it so much.
Bob

 

[SternWake]

I've been thinking more on this question and thought I should add some more info.

High temperatures and hard vibrations will also degrade a battery much faster than a cool still battery.

I personally saw my always fully, or very nearly so, engine compartment battery, to be a waste.

I.ve actually lowered my overall capacity with a smaller house bank. But that term is now almost irrelevant, since I can now use either of two batteries as engine starting or house at the flip of a switch, or three.

since I have many methods of determining how much battery I am using. , I have little concern about being always able to start my engine. Also one of my batteries is an agm. I depleted it more than 2/3 the other night, and used only it to start my engine. I could barely notice that it spun the starter any slower.

From now on, in my van. All batteries will be cycled. I am not going to carry around a fully charged battery just for engine starting. I am not recommending others do this unless they can measure the amp hours removed from a battery, or carry a jumper pack

 

[Optimistic Paranoid]

I appreciate you and Bob taking the time to share your insights on this.

Let me mention one more thing.

The original recommendation came from the Hellroaring Battery Isolator site.

They pointed out that, in addition to starting your 4x4, a spare, fully charged battery could also save your bacon in the event of an alternator failure when you are way out back of beyond, since it could power the ignition long enough to get you back.

Obviously, a kind of special situation that wouldn't apply to most people, but valid for the few who might need such capability, I think.

Regards
John