does listening to the radio w/o driving ruin a car battery

i think this is a factual question and not an IMHO question. if not i guess someone will move it.

I like to sit in the car with just the electric power on & listen to the radio sometimes, maybe for 10-20 minutes or so. i know that the alternator recharges the battery when i drive but are standard car batteries designed to be deeply drained (by listening to the radio w/o driving at the same time to recharge) then recharged, or just mildly drained & recharged? Does a deep recharge (taking too much power out of the battery, like 60% or so) then recharging do more damage than a light recharge like taking 10% out then recharging it?

You realise a portable radio works on batteries which are tiny compared to a car battery? You could listen to the radio in your car for hours and it would i=only use a fraction of the baeery power.

Unlike deep-cycle and marine batteries, automotive batteries suffer from being more than slightly to moderately discharged. So yes, 60% discharge does significant damage to a car battery, and will significantly shorten its effective life.

From here:

Automotive, or SLI (starting, lighting & ignition)
SLI batteries are commonly used to start and run automobiles, where a very large starting current is needed for a short time. SLI batteries have many very thin plates with a large surface area, designed to be discharged no more than 1 to 5% from full charge. These can be damaged quickly if deep cycled.

Marine / Deep Cycle
Deep cycle batteries are designed to be discharged down as much as 80% time after time, and have much thicker plates.
The so-called Marine deep-cycle batteries are actually a “hybrid”, and fall between the SLI and deep-cycle batteries. These should not be discharged more than 50%.

Using the radio for an hour at moderate volume would use about 1% of the battery capacity and is absolutely safe and will do no damage to the battery.

Compare that with leaving your parking lights on which use quite a bit more juice . And then compare that with leaving your headlights on which use a lot more juice.

You can listen to the radio for hours and that will not do any damage to the battery.

I think the car talk guys covered this one recently, too. People who go to Drive-ins have the same question.

You’ve got plenty o’ juice; no worries.

i dont want to use a portable because i listen to the CD player and don’t have a skip-proof cd player or portable speakers. plus my vehicle has a very nice radio with high bass, easy to manipulate buttons and surround sound speakers.

My car radio shuts off automatically if I leave it on too long. I think it’s 30 minutes. I imagine that’s just a fail safe. I just have to turn the key again.

Back in the good old days car radios had vacuum tubes and cars had much smaller capacity 6 volt batteries. A car radio had 6 maybe 6 tubes each of which had its own heater which used a really significant amount of power. And then a couple hours of radio usage would drain the battery. Nowadays, they use transistors, which use a trivial amount of power by comparison. I imagine it would days to drain the battery, although if it is really true that even a 5% drain can damage the battery, then maybe you do have to be careful.

On newer cars, the radio turns off when the car door is opened, not when the key is taken out.

In my car you can turn on the stereo for one hour without even putting the key in the ignition. Obviously they feel an hour is safe. My battery died a couple of weeks ago (nothing to do with this conversation) and the guy who replaced it told me that the average life of a car battery is only 41 months. That surprised me but since the guy sells 500 a month I guess he knows what he’s talking about.

Also depends on the system. A couple of big amps and subs and it is possible to drain a battery to the point where a car might not start.

Deffenetely. I killed my old car’s battery within 30 minutes of blaring some tunes. I had a 300watt amp and another 100w from the deck. Is there any kind of equation we can use with watts x time that can show how much can be drained?

Car batteries are traditionally rated in ampere hours. Divide your watts by the voltage (12) to figure how many amps you’re drawing, and then multiply those amps by the hours involved to see how ampere hours you’ve used.

You have to take efficiency into account, also.