Second battery for long-term health

[JHZR2]

As some know, I work in battery technology, amongst other areas. But I am not an EE, so am thinking out loud here...

I own seven cars and some of them do not get use in the winter (maybe once or twice over many months). One of those cars gets kept in a garage that is in a shady spot and does not have electricity. So keeping a battery tender type of device, even a solar one, isnt a straightforward proposition. Turning on and running a vehicle until a battery is truly fully charged (constant current then constant voltage until the current is, say,
While Im likely to do that, its the intermittent swings where both self discharge, thermodynamics of cold weather, and parasitics of the vehicle draw down the battery voltage to a point where sulfation and other bad things can occur.

One of the first things I do on my vehicles is add an SAE 12V connector, which is the standard interface for the Battery tender and minder brand chargers, so I have these connections...

So my thought is to connect a second 12V battery via this conenction, ONLY for the purpose of having double energy for the time spent sitting.

It would be fuse protected on positive and ground, at the second battery, for say, 2A. It would be connected after the car is shut down, and removed before the car was started.

So the only issue is that the two batteries would over time and over vehicles be different in size and capacity as compared to the installed battery in the car. Notionally the car would always be put away with a full battery as is my practice.

The intent here is just to roughly double the duration before the car's battery got sulfated or damaged. Concerns or issues????

Thanks!

 

[The_Jeff]

My first thought would be to look at say a diesel pickup and how they balance loads across dual batteries. What causes eventual battery death, and do people typically replace them in pairs like they should?

If one is weaker it can take the other one down. So you'd want to start with two fresh batteries.

Of your seven cars, do any of them share a battery shape with the one in cold storage? Maybe you could make a trip up in mid-winter and just swap them.

The elegant solution would be a self starting generator that ran for an hour a week, coincidentally charging your car. Maybe you could get one of those roadsize "arrow" light-up sign trailers that are programmed to start up and charge their own batteries. Or a marine bell buoy. Start hitting the state surplus auctions!

 

[JHZR2]

LOL good ideas!!!

The parallel diesel batteries dont particularly relate because Ill not have a big load on both, like starting, that can force one cell into reversal, nor will they be charging together. Ill only connect the two up by the SAE plug when the vehicle is completely off and locked up/asleep.

One could be weaker and hit a lower voltage, but if that delta is high enough to cause a substantial current draw from the supplementary battery, it would blow the 2A fuse, and it would be obvious that something else was wrong. If not, then the two will keep each other roughly in check.

And if the parasitics are some value, having 1.5-2x more energy should mean more runtime.

The key thing here is that they arent being charged at the same rate or discharged together at all... So it seems benign.

 

[rjundi]

Disconnect the battery when not in long term use. It will last years. My father has a 1990 4runner with 150k miles that has a 12 year old die hard. He never drives in the winter(buried in snow) or summer(broken AC).

You are overthinking it.

I believe he had some sort of connector installed where he pulls a pin with a leash to disconnect it.

 

[Kuato]

Interesting theories, but seems like a lot more work than simply bringing the disconnected battery inside to warm conditions for a few months.

 

[wrcsixeight]

I did not know those were called SAE 12v connectors. I use them in a lot of places.

If I understand your intent right you basically want to parallel another battery so that the parasitic draws take a lot longer to bring both batteries below 80%, when the sulfation starts and begins to harden.

I don't see why this would not work. I don't know how much time will pass before the 80% threshold is crossed, but no doubt it will increase that time.

I'd say for the older vehicles just to fully charge the battery and disconnect the Ground cable, but perhaps newer vehicles don;t like to have their PCM unpowered for months on end.

The only issue I see with parallelling another battery through a SAE 12v connector is that one could easily blow a 2 amp fuse if the batteries are even a tenth of a volt difference, and fuses are not cheap, and perhaps you would not notice it had blown.

Also it is said to be much better not to parallel batteries of different makes and ages, and let them discharge together.

How quickly the weaker battery would reduce the capacity of the stronger would be hard to say.

A possibility is having an old school manual charger on a timer. Feed the battery 10 amps or so for a half hour once a week, but if you are running AC out to a vehicle, then the temp compensated maintenance chargers, as you are aware, are the way to go.

 

[nitehawk55]

If the car(s) that will be sitting are non computer and power isn't nearby the simple solution would be remove the battery and trickle charge over the winter .

 

[JHZR2]

Yeah right now for example I have my 135i out there. It likes to suck down the battery. Of course its as simple as swapping cars parked there, but sometimes I have different cars in different spots for different reasons.

Because the load is so low, was the only reasoning I could use to justify mismatched batteries. We never would do so with anything that would support real load. But since I know that all cars can be maintained just fine with a 1.25A charger (less actually), and parasitics are quite small, well, that was my only basis for this being "logical". Pulling batteries in and out of cars all the time is undesirable, especially since I do try to use them as much as I can, even in the winter.

 

[nitehawk55]

If the battery is in good shape then just disconnect it or get a long extension cord and use trickle chargers/battery maintainers .

 

[DoiInthanon]

My solar tender works just fine in the deep woods for my woodlot truck. Disconnected from the vehicle and scrubbed clean the battery stays in good shape. If I need the truck, it is a matter of a couple of minutes to pop the hood, unhook the solar, and reconnect the cables.

 

[friendly_jacek]

Originally Posted By: Kuato
Interesting theories, but seems like a lot more work than simply bringing the disconnected battery inside to warm conditions for a few months.


Nice try, but battery will discharge and sulfate sooner in warm conditions. Battery is like food. Likes cold for long storage and spoils fast in hot.

 

[friendly_jacek]

Originally Posted By: DoiInthanon
My solar tender works just fine in the deep woods for my woodlot truck. Disconnected from the vehicle and scrubbed clean the battery stays in good shape. If I need the truck, it is a matter of a couple of minutes to pop the hood, unhook the solar, and reconnect the cables.


+1. I do that in my boat at seats in shade.

 

[Rob_Roy]

How big of a job is it to run 120v to the building?

 

[The_Jeff]

I suspect OP is looking for an engineering exercise that doesn't involve running AC power.

Maybe the car is in self-storage and the landlord wants another $30 a month for power for example.

I also kind of like the solar panel idea. It might not be perfect but it'll slow the rate of decay. One designed for 12 volt systems has an open voltage way over 12, but put any sort of battery on it and it brings it down. One just needs enough shady sun to hit ~13.5 or more and it'll do some sort of work.

If the garage is dark but has those little door windows, run extension leads.

Of course if OP likes security the solar panel might say, hey, come in here.

 

[johnachak]

Originally Posted By: JHZR2
As some know, I work in battery technology, amongst other areas. But I am not an EE, so am thinking out loud here...

I own seven cars and some of them do not get use in the winter (maybe once or twice over many months). One of those cars gets kept in a garage that is in a shady spot and does not have electricity. So keeping a battery tender type of device, even a solar one, isnt a straightforward proposition. Turning on and running a vehicle unntil a battery is truly fully charged (constant current then constant voltage until the current is, say,
While Im likely to do that, its the intermittent swings where both self discharge, thermodynamics of cold weather, and parasitics of the vehicle draw down the battery voltage to a point where sulfation and other bad things can occur.

One of the first things I do on my vehicles is add an SAE 12V connector, which is the standard interface for the Battery tender and minder brand chargers, so I have these connections...

So my thought is to connect a second 12V battery via this conenction, ONLY for the purpose of having double energy for the time spent sitting.

It would be fuse protected on positive and ground, at the second battery, for say, 2A. It would be connected after the car is shut down, and removed before the car was started.

So the only issue is that the two batteries would over time and over vehicles be different in size and capacity as compared to the installed battery in the car. Notionally the car would always be put away with a full battery as is my practice.

The intent here is just to roughly double the duration before the car's battery got sulfated or damaged. Concerns or issues????

Thanks!


Ok, I might have missed something here, but, why not just use plug in battery tenders? You could probably hook up 6 of them to a single outlet and not go over 10 amp draw under the worst conditions?

 

[johnachak]

And you don't think that is too old for a Diehard? They certainly aren't the top of the bunch. I have warrantied more Diehards than any other batteries.

 

[johnachak]

Originally Posted By: friendly_jacek
Originally Posted By: Kuato
Interesting theories, but seems like a lot more work than simply bringing the disconnected battery inside to warm conditions for a few months.


Nice try, but battery will discharge and sulfate sooner in warm conditions. Battery is like food. Likes cold for long storage and spoils fast in hot.


????????
I bring my boat batteries in for the winter, put them on tenders and in the spring they are ready to rock.
I would love to know where you heard that they would "spoil". Only guys that leave their batteries in the cold seem to be the ones with battery problems in my experience.

 

[johnachak]

He's talking about 7 cars IIRC.

 

[Billy_D]

Originally Posted By: rjundi
Disconnect the battery when not in long term use...


+1

You can get a battery disconnect switch at any RV parts store. It's the most effective way to to prevent battery drain.

 

[andyd]

Batteries like cold weather as long as they are charged. The Rat has a small but newish 2 yr old Valucraft. It spent its first winter, New Year's to April 15th, disconnected. It started the truck easily. when I was done with the project. The new battery in my sit down which sits in an unheated shed will probably start the engine next spring.