That recommendation is both contemptible and ridiculous.
An Aged battery only requires a fractional amount more amperage than a new battery to be held at the same voltage.
And if the newer battery were unintentionally discharged, it would demand much more amperage from the alternator than the aged battery to be brought and held to the same voltage.
The misunderstanding of the realtionshop between voltage and amperage that a battery can accept, by most every mechanic, is a bit infuriating when I see these asinine recommendtions by people who simply do not understand, who have never seens an ammeter and what a battery can accept at different voltages and different states of charge.
While short trip driving will never be able to fully recharge a depeted battery, the actualy amount of electricity used to start a modern fuel injected engine takes less than a minute for an alternator which is commaded by its voltage regulator, to bring the battery over 14 volts after starting.
i am apporaching 6 years of age on an AGM battery with over 1000 deep cycles, many thousnads of engine starts.
achieving excellent battery longevity is ALL about proper prompt recharging to full.
Heat does of course play a role, but batteries are murdered by living chronically undercharged, and this is usually becuse of timid voltage regulation, and the fact it takes no less than 3.5 hours, it higher voltages, for an healthy 80% charged battery to get to 100%. This cannot be sped up safely. It is a simple fact of lead acid batteries. No less than 3.5 hours required under ideal voltages to get from 80% to 100% charged, and ideal voltages for fastest recharging are in the mid to high 14's with a 77F battery.
The battery accepts what it wants at the voltage allowed by the voltage regulator, and the closer to full it is, the less amperage it accepts, or to look at it a bit differently, the less amperage is required to maintain that constant voltage.
A aged battery below 80% state of charge will require less amperage from teh alternator to maintin charging voltages, compared to a new one.
The new battery near 100% state of charge will require less amperage than the older one to be held at higher voltages, but the difference is an only 1 to 3 amps, unless there is a shorted cell.
1 amp at 14 volts is 14 watts. Many cell phones will accept 14 watts when charging .
Gee better not try and charge your cell phone while driving as it will overload the alternator.
Freaking ridiculous!!