Charging/discharging a 12V car battery?

[jeff88]

I was just wondering how long it would take to charge a 12V car battery. Obviously it would be dependent on amps, so really the question is how long & how many amps. I'm thinking if I "plugged-in" to my house outlet (like a GFCI), what/how long it would take. I would eventually like to plug into a solar panel at some point as well.

Also, without an alternator and no charging at all, how long can I drive a typical passenger car (like my Toyota Corolla) before the battery dies. I'm not looking for concrete numbers, more of less than a day or almost a week type figures, ballpark.

Thanks!

[oil pan 4]

Starting batteries are not deep cycleing batteries. The are made to start the engine, get charged up and handle minor momentary loads that are too much for the alternator to handle. Your best bet is to get a deep cycle battery and the proper charger before you start any of this alt delete stuff.
The starting battery wont last long at all doing this.

[Ryland]

Average car starting battery is 40 to 60 amp hours when it is new depending on the size of the battery of course.

In theory you could charge a 40 amp hour battery in 4 hours with a 10 amp charger, but if you drain a 40 amp hour battery down 100% you've damaged the battery and you're never going to get it to hold 40 amp hours worth of energy again.
Older dumb battery chargers also only charge at their rated output when the battery is deeply discharged, as the battery reaches a fuller state of charge the energy going in tends to taper off, so a 10 amp charger might be putting 3 amps in to a battery when it's 80% full, this is of course good because absorption of the charge is needed and over charging causes the battery to boil and loose electrolyte (add distilled water) smart chargers can dump energy in to the battery faster and once they see the voltage top out they lower the amps going in and hold it at a set voltag, this boils the battery less and allows for a faster charge, it also requires a more expensive charger.

If you are charging over night tho, a 2amp or 5 amp charger that can float should work great.

Deep cycle batteries are not an ideal starting battery and starting batteries are not good with deep cycle loads, I don't see anything wrong with pairing a deep cycle battery up with a starting battery, the cable connecting the two will limit the energy from the deep cycle battery while starting and of course the load is split between the two so even under starting the starting battery will not be discharged as hard and the deep cycle will bring the starting battery back up a bit after the vehicle is running.
Other option that is even better and costs even more is a higher voltage deep cycle battery pack, a regular starting battery, and a dc/dc converter, this will allow the starting battery to be fully charged after starting, bringing it's voltage back up to 13.4v in the same way the alternator would, this will make your head lights brighter and put less stress on the rest of the electrical system.

[bobo333]

I use Optima batteries in both of my cars which are deep cycle but still have a high enough CCA for starting

a quick way of getting an idea of how long you can drive is to add up all of the fuse values on the electrical items you will be using, then divide it by the amp hours on the battery

ie if you are using a radio (10a) head/taillights (15a each) and demister (15a) you could drive for at least an hour on one of the D34 size Optimas (55ah)

***this is only a guestimation, these values are made up so check you actual values

Also fuse values are max power draw so for something like the radio it will draw much less if you turn the volume down***

It would be wise to install a voltage guage in plain sight on your dash and watch it while your driving, anything below about 10.5 volts and your gonna have trouble with your electrics, plus the car wont start anymore... as long as you charge it before it gets this low the battery should last ages

[brandgill]

I also use the Optima batteries as these have got a good starting power. These also help in got pick up of the car.

[some_other_dave]

Charging:
- Overnight seems to work reasonably well in a battery that has not been too badly discharged.

Discharging:
- If you're driving during the day, and not starting/stopping much, an older car can run for a day off a fully-charged battery that gets recharged overnight.
- A newer car needs more electrical power than an old one, because newer cars have a lot more electrical doo-dads to consume power. Plus a number of those systems are more sensitive to the voltage droop that will happen as the battery gets discharged. (Example: I ran an old car until the voltmeter dropped below 9V when the alternator failed on me. Later, after swapping in an electronic ignition for the points, I had another charging failure. The car died when the voltmeter dropped to 10V.)

Unfortunately, I think the real answers in this case are "try it and see".

-soD