Recharging car battery

The length of start is only seconds. 10 amps times 20 minutes equals 1200 amp seconds into battery. 1200 divided by 3 seconds equals 400 amps for 3 seconds out out of battery. Might be right or wrong, it's late.

Alternator must be higher in rpms to deliver anywhere near max output, so driving is better than idling.

Greg

A typical BMW Bosch alternator is 120 amps (160 for the higher performance bimmers). That's a LOT of current.

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The alternator has a much higher output than the typical battery charger so it does not take very long to get it up to snuff again. But discharging like that is not good for overall battery life.

Do you have a very old car? I think it was in the 70's that most cars had a buzzer to let you know the lights were left on. For quite a few years now, automatic lights have been available.

doesn't even have to be driven to recharge battery enough to drive and be able to shut off and start again? This has been bothering me for years.

Good answer. Most car alternators have good output, even at idle. I've read and heard that deep discharges are damaging to car or other lead acid batteries. So, leaving lights on over night will shorten the lift of the battery, and may kill it totally.

Perhaps HB might be wise to buy a car battery charger, and have a neighbor show her how to use it? You could run extension cord from the house, and put the charger on. Faster than the response time of the tow service.

It might be worthwhile to have a mechanic install a relay to automatically turn off the lights when the ignition is off. My Subie has it and it's a nice feature.

Higgs Boson wrote in news: snipped-for-privacy@googlegroups.com:

Well, the root problem is that you are a moron. That is shown by

2) You post through GGs.

Get a clue dude.

As mentioned, the car's alternator has considerably more output that your typical "home" charger. In 20 minutes it would not fully charge the battery...more than likely 80%. Of course that would be good enough to start the car quite a few times.

A lot of cars have the "turn off feature"

BTW: A 10 or 20 amp battery charger would be a good thing to have. It would cost less than a service call and would probably only take a short time to charge the battery enough to start the car.

I have a battery tender for the bike , it takes about 24 hours to recharge the truck if I forget and leave lights on . I also have the old charger/power supply from the camper . It puts out 55 amps , and will charge the battery enough to start the truck in under 30 minutes .

Since I worked in the battery industry I managed to accumulate a lot of surplus gear. I have one charger that puts out about 120 amps and can start a car with a dead battery. Of course it's very heavy and though on wheels, has only been used in emergencies.

If you forget to turn the lights off, would you remember to plug in the charger? Maybe the world needs a wireless charger so you would just have to remember to park the car in the same place.

Higgs Boson wrote in news:839b0b67-1939-4c1c-b754- snipped-for-privacy@googlegroups.com:

Years ago, when I got to work I noticed another car in the parking lot with its lights on. I called our security office to have them locate and notify the owner. One of my coworkers overheard, and said that he *never* tells anyone they left their lights on. Says he's being more helpful that way. How do you figure that, I asked him. He asked me "Did you ever leave your lights on, and come back to a car with a dead battery?" Well, yes, of course, but -- "Did you ever do it again?"

I guess some people don't learn as quickly as others.

If you turn the key and the battery is dead, that's a good reminder to 1) ring bells, ask a neighbor for a jump, 2) call tow service. I'd think she can remember 3) get out the charger and extension cords.

they should make a battery charger with a built in coffee maker to save you the trip back to the kitchen while you wait.

Have relay installed to turn lights off when ignition is off

REPLACE the existing battery its been damaged by deep discharge, espically repeated deep discharges!

I replce my vehicle batteries every 3 years and buy only premium batteries.

since doing this alternator replacements are very unusual. The added work of charging batteries in poor condition and deep discharges! damages alternators

The cost of replacement every 3 years is actually pretty low, plus I give the still OK replaced batteries to a buddy with a 12 volt windmill system

MOST alternators will put out about 80% of maximum output at"cold idle" speed - unlike generators with about 5%. 20 minutes of idling will put enough charge into a battery to restart the engine, but a FULL charge takes over an hour of running.( in some cases, from dead, over 2 hours)

General rule of thumb. Each time a battery is run dead, you lose half the life of the battery. So do it twice, you are down to 1/4 life. This was particularly true of the Delco "freedom battery" which was, if I remember correctly, a high calcium battery. Today's batteries may be slightly better (or worse).

MOST decent battery chargers have a "start assist" or "boost" mode that will start most engines after only a minute or two.

Some chargers have a "jump start" option too.