Request for Question Clarification by
02 Oct 2005 17:04 PDT
Well, from what I've found, it's true that a single discharge
of the level you're describing won't kill a good battery, but
it won't do it any good, either, and if the battery is weak,
obviously that can push it to the point of no return.
In simple language, the more often a battery is discharged,
the shorter it's life, and the older the battery is, the
more likely it is to be discharged to a damaging degree.
Relevant factors include:
"Never discharge any 12-volt lead acid battery below 10.5
volts because it can damage the battery."
"Leaving your lights or other accessories on and fully
discharging a car battery can ruin it due to 'cell reversal',
especially if it is a sealed, wet Maintenance Free (Ca/Ca)
Cell reversal is where one or more cells in the battery
actually change polarity.
Obviously, this is more likely to occur with a weaker battery.
...from a very thorough discussion of battery life expectancy
on William Darden's site:
Another factor is the quick charge you're giving the battery
to restore it to health. Quick charging does more harm than
"Fast recharging at rates greater than C/4 (amp hour
...is a (low on the list) cause of premature battery failure,
per this page on the most common causes, on Darden's site:
Then again, old age is equally low on the list, and the main
cause (repeated 3 times) of premature battery failure is:
"Water Loss! (Car) and Sulfation! (for batteries not used weekly)"
"Sulfation from water loss, undercharging, electrolyte
stratification, excessive temperatures or prolonged periods
of non-use account for approximately 85% of the deep cycle
and starting battery failures that are not used weekly,
vehicle charging systems based on driving habits (short
trips with high loads leaving the battery constantly
Water loss can occur even in sealed "maintenance-free" batteries,
so refillable batteries are recommended in hot climates.
Another factor influencing water loss is that car engine
under-the-hood temperatures run about 30% higher now than
they did 20 years ago.
Much more on the page:
Given all this, I would recommend hooking the charger up
*while* you're servicing the car, assuming it can handle
the load of the door lights (and radio?) in addition to
providing some charge to the battery. This would act as
a preventive measure to ensure you have no more failures.
Searches done, via Google:
"a car battery dies"
Since what I found provides a mixed interpretation of the
effects of your current practices, I won't post it as the
answer you'd obviously prefer to receive, unless you are
happy with the facts even if they don't entirely let you
off the hook.
Let me know what you think...