Quick Battery Question

[jameselmore]

I'm sure this a question which is easily answered I just wasn't sure what to search on google to get the answer I was looking for.

Tonight I plan on going to a drive in movie with a date and they advise that I just leave my car in Auxilary mode without running the engine just so I can hear the audio over the radio. They offer free jump starts if needed.

Is it bad practice to intentionally run the battery dead?

Should I do as they advise? Or should I avoid any kind of damage to the battery by running the car every once in a while?

I'm driving a rental so I don't really care a whole whole lot about the battery of the car but if it is something that may have long term effects I wouldn't want to impose them on the rental company.

[Alphabravo]

I'm not sure what the reprecussions are from fully discharging a lead acid battery, it probably won't hurt if it's not done on a regular basis. You can probably google "lead acid battery discharge" and see what you get.

I would be more concerned about the jumping process. Check the owner's manual because some cars you will have to pull a certain fuse before you jump it or jump another car with it.

[MagicRat]

Don't run a regular lead-acid battery down totally flat. They lose about 10% of their power each time you do that. The lead plates build-up a deposits of sulpher on them (from the battery acid) thus reducing their effectiveness. I suspect though, this varies depending on battery design and age. Partial discharging causes no harm, of course.

It's also hard on the car alternator recharging a battery from this condition.

"Deep Cycle" lead-acid batteries, for marine and RV use are designed to be repeatedly discharged and recharged repeatedly without damage.

[mhr430]

First, unless we are talking about a disposable battery, it is never good to run a battery dead. Never. Saying that it "probably won't hurt if it's not done on a regular basis" is wrong. Don't do it. As far as saying that running a battery dead causes it to loose about 10 % of anything is also incorrect. I've seen brand new batteries of several different types (lead acid, NiMh, nicad, lithium and others) become forever unusable after running them dead only once. That's why running a battery dead is called running it dead!

Now as for following the drive-ins instructions, although it's not the best for the battery and assuming that since it's in a rental that it's fairly new and in good shape and that the stereo isn't going to pull massive current, you should be o.k. without needing a jump start. I could show you the math on it but I'm sure that you're not really interested right now.

Finally, just a little extra FYI. The best way to get a long service life from your battery(s) is to discharge them as little as possible before recharging; recharge as soon as possible (unless the battery is overheated); use the correct charger; always fully charge before storage; avoid harsh conditions (temperatures that make people uncomfortable and vibrations unfortunately car batteries must live with these). I've seen nicads that the manufacturer says will last up to 500 recharges last for 9 years with daily use just following these policies and I've seen lithium batteries that nominally have a life of 5 years or less last for nearly 14 years!

There's a lot more info about batteries if you're interested. One good place to start is at http://batteryuniversity.com/ There are others that have more info and are a lot more technical but this one has much more info than most people need and it's easy for just about anyone to understand.

Good luck.

[Scrapper]

Originally Posted by jameselmore

I'm sure this a question which is easily answered I just wasn't sure what to search on google to get the answer I was looking for.

Tonight I plan on going to a drive in movie with a date and they advise that I just leave my car in Auxilary mode without running the engine just so I can hear the audio over the radio. They offer free jump starts if needed.

Is it bad practice to intentionally run the battery dead?

Should I do as they advise? Or should I avoid any kind of damage to the battery by running the car every once in a while?

I'm driving a rental so I don't really care a whole whole lot about the battery of the car but if it is something that may have long term effects I wouldn't want to impose them on the rental company.

i know it's good for cell phone to let it go almost dead until you plug it back in. if your battery is not sealed if you check water in battery and use distealed to do so. also look at posative side of battery if it's white it's because your alt. puts out to much volts that the battery cant handle.

[mhr430]

Scrapper, I know you mean well and want to help but please look at the link that I provided earlier. It is just one of many sites that confirms that running a battery dead or almost dead is bad for the battery. This is a general rule for all batteries. You should never run your cell phone battery almost dead, or any other battery, unless it is a nicad. I'm not aware of many phones nowadays that come with nicads, most are lithium. See the rule that says dead means dead. The only "exception" to this rule is the nicad when it comes to what's called a charge memory but this is exactly why nicads are rated at only up to about 500 charge cycles for the best of them. This limited life span and the fact that most people ran nicads almost dead before recharging them and then being upset that they only got a few weeks or months use out of a battery that's more expensive and more work than the standard coppertop or bunnycell is why it is nearly impossible to find nicads on the store shelf for much more than your cordless house phone.