Learning about car batteries

[Thorin]

I've been having a bit of trouble with my Suburban's battery.  We'll park somewhere, let the accessories run for ten minutes or so with the engine off, and then the car won't start.  Today it actually wouldn't start after being parked without us having ran any accessories!  My poor wife was stranded for twenty minutes waiting for Roadside Assistance.

Rather than spend time and money figuring out what might be wrong with the factory battery, we decided to just buy a new one.  Afterward, I found myself drawn to all kinds of useful information about how batteries work and what kills them...

Acid stratification, a problem with luxury cars

A common cause of battery failure is acid stratification. The electrolyte on a stratified battery concentrates on the bottom, causing the upper half of the cell to be acid poor. This effect is similar to a cup of coffee in which the sugar collects on the bottom when the waitress forgets to bring the stirring spoon. Batteries tend to stratify if kept at low charge (below 80%) and never have the opportunity to receive a full charge. Short distance driving while running windshield wiper and electric heaters contributes to this. Acid stratification reduces the overall performance of the battery.

Figure 3 illustrates a normal battery in which the acid is equally distributed form top to bottom. This battery provides good performance because the correct acid concentration surrounds the plates. Figure 4 shows a stratified battery in which the acid concentration is light on top and heavy on the bottom. A light acid limits plate activation, promotes corrosion and reduces performance. High acid concentration on the bottom, on the other hand, artificially raises the open circuit voltage. The battery appears fully charged but provides a low CCA. High acid concentration also promotes sulfation and decreases the already low conductivity further. If unchecked, such a condition will eventually lead to a user-induced battery failure.

[..]

Allowing the battery to rest for a few days, applying a shaking motion or tipping the unit over tends to correct the problem.

I thought the mechanic was loonie a month ago when he told my wife that tipping or banging the battery can cause it to suddenly start working again, but after reading the above it suddenly makes sense!

Our car has lots of current-draining gizmos (power windows, power seats, power mirrors, power sunroof, seat heaters, TV, plug-in inverter charging the cell, etc) that all get used often, and sees a lot of shorter trips, so the bit about the battery never receiving a full charge and therefore dying more quickly is probably very apt for my situation.

Still, I could get my battery to work again if I give it a good shake?  Seems weird, yet makes sense now...

[Lazybones]

Leading cause for my battery problems has been, bad alternator or old battery. Given how new your car is I am VERY surprised the battery is already toast unless all your driving is under 30 min per trip.

[Thorin]

I'm not surprised as it's a high-mileage unit imported from eastern Canada.  I fully expect there to be several thousands of dollars in repairs it needs.  In fact, I've already passed the two-thousand-dollar mark, I think.  Much of that was covered by extended warranty, though.