Road car batteries in zero mileage times

I'm a low mileage driver and I keep a mental check of how long since I took a long journey. And I am very quick at yanking a lead acid battery for charging. Are my experiences representative and am I missing any tricks?

My rule of thumb is that a fairly new battery (> seven years old) will hold enough charge to start the engine 14 days after last run. Long enough to park whilst you take your annual holiday. Older batteries discharge more quickly. If you have access to a de-sulphation recharger, you can extend battery life and charge duration.

Modern cars may not generate much of a recharge when stationary and ticking over. I have found that ten minutes on tick over is about enough for a reliable start a few days later, but not enough for a week. A ten mile drive on open roads once a week keeps the battery alive but a supermarket shopping trip is insufficient. 

I have a car that gets driven only occasionally. The battery was getting a bit tired and was often too weak to start the car after a few weeks layover. Too mean to buy a new battery, I installed a "charging" point (an RCA jack) in the glove box. This made it simple to plug in a home made trickle charger (an old plug pack with appropriate resistor in series) whenever the car was home. Worked a treat.

Bought a new battery recently and haven't been plugging in the charger much.

... a fairly new battery (> seven years old) ... 

'<'?  More than 7 years old around here would be 'pretty damn old and ready to let me down'.

The lead-acid in my old Falcon is trouble free, even when parked outside in cold (0 to -10) winter nights, but it is only a few years old.  The toy has an AGM and if isn't getting much use it goes on a trickle charger, for which (like GG) it has the leads and a plug permanently attached to the battery.

My old Dad - long gone, sadly - had an adage about car batteries.  He wasn't prone to adages so I tend to remember the few that he uttered. 

'Measure twice, cut once' 

'If a job's worth doing, it's worth bodging'

and (to get to the point at last)

'Don't muck about with old batteries - if it is going flat, get a new one'

In my experience the only valid rule is: "it depends"

My pretty new (less than 1 yr) daily driver sucked its battery empty when I had it parked for 20 days due to Corona induced massive reduction in car use.

The 15 yr old Sears battery of my Cadillac finally got tired last fall; the no-name replacement died within two weeks with the car being used once or twice per week.

A 4 yr old original Nippon Denso battery of my Supra died; it's no name replacement still survives.

The no-name battery of my previous daily driver lasted 8 years with plenty of abuse (stand-alone heating, forgot to switch off the lights...).

I can't derive any principle from these experiences.

Principles:

1. Battery life is unpredictable

2. No-name batteries more-so

A 7y/o battery is prehistoric. A top quality battery is 4 years normally. Early autumn is what usually kills them. Those cold mornings

Modern cars have so much happening when turned off that batteries have more reserve and even then about 10 days will stop them.

Either that or disconnect the battery.

Plus even worse too many modern cars have the alternator not charging at low rpm so they can show more MPG.Late Landcruisers a bad example. First thing many do is get the charging modified so as not too have flat batteries.

In my experience the only valid rule is: "it depends"

 

My pretty new (less than 1 yr) daily driver sucked its battery empty when I had it parked for 20 days due to Corona induced massive reduction in car use.

 

The 15 yr old Sears battery of my Cadillac finally got tired last fall; the no-name replacement died within two weeks with the car being used once or twice per week.

 

A 4 yr old original Nippon Denso battery of my Supra died; it's no name replacement still survives.

 

The no-name battery of my previous daily driver lasted 8 years with plenty of abuse (stand-alone heating, forgot to switch off the lights...).

 

I can't derive any principle from these experiences.

   15 year old battery?     Shirley Knott.  

I had an OE one die at 12-13 years. It was fine until that point then one day it was utterly dead.Holden (ie Opel) Astra. The fact that it was twice the size of a normal battery may be something to do with that. My guess is that it was specced for East European winters and so had a very easy life in Oz.

More than 7 years old around here would be 'pretty damn old and ready to let me down'.

OK, it was a guesstimate and based on comments, there is no easy way to guess how long a modern battery will be functional. Those old batteries with thick plates lasted a long time (versus lower energy density per kg) and I used one in a Saab for 20 years...

Plus even worse too many modern cars have the alternator not charging at low rpm so they can show more MPG.Late Landcruisers a bad example. First thing many do is get the charging modified so as not too have flat batteries.

Not charging the battery at tick over seems to be a poor design compromise to me, but thanks for the reminder about what happens, Lee. It's more likely that the alternator is charging the battery at a lower rate than consumers consume. The first thing I do after starting the engine is turn on the radio and curse that I live in a reception blackspot.

Not charging at idle doesn't sound like a viable fuel saving measure to me. A few hundred watts added to engine load at idle would be provided at high marginal fuel efficiency - probably more efficient than adding the same recharge energy while the engine is loaded. Are we talking 0.0001 mpg? I am calling BS.

It is nowhere near as cut and dried as that. If you give your car to the 'experts' in the motoring press they often do a group test, over which the manufacturers have no control at all. If your car has the best claimed mpg, but the worst group test mpg, of the cars, then you can and will get called on it, at least in less obsequious cultures. One fun job was to hire a couple of competitors and take them, and your new pride and joy, out for a couple of days of fast driving, just to check that this wouldn't be the case, or, if it was, to get the spin doctors prewarned, I suppose.

Real world fuel consumption is a significant, if not dominant, contributor to the accurate total cost of ownership of the car. That's what the fleet buyers are interested in, so the more fuel your car uses in practice, the less they'll pay for the car. That is actual real dollars the manufacturer will see as a penalty, should they be daft enough to be interested in fleet sales.

Remember fuel saving measures is not about fuel saving but cheating the test.

Maybe, but I am saying not charging at idle won't help the test (or the real world economy).

Here , new batteries have a 2 year warranty/guarantee . the purchase date gets etched or scribed on the case by the dealer

The average lifespan is 2 years and 1 day 

Then , how average is the average battery lifespan ?

Batteries in Canuckistan typically have a pro-rated warranty after a given number of months. My E28 had a sporadic electrical draw that would kill the battery if left for a weekend, but only some weekends. A bunch of testing narrowed it down to something in the electric door lock circuit but I never did find out what. That short killed a couple of new batteries when the car sat idle for more than just a weekend.

The wife's RX hybrid has an almost motorcycle-sized 12V battery that has a relatively short lifespan. I want to say we've had it for 7 or 8 years now and I've replaced the battery (that was new when we bought it) twice since. The big old Expedition battery is on it's 5th year despite the annual 2 - 3 week dips below -30° C each winter.

I am at that point now where if I know the vehicle will sit for a week or two, I disconnect the battery, and what got me to that point was my fancy battery charger.  I hated that thing.  It would kill a motorcycle battery unless I also connected a car battery in parallel, and it refused to even talk to a mostly discharged battery, it just flashed its fancy microprocessor-controlled display and told me to buy a new battery.  I dug out my old charger, does not even have an on/off switch, nothing inside but a transformer and a rectifier, works every time.