How long does it take a car battery to become fully charged?

Question

I don't use my car often. I only do 500-1000 miles a year. The car can be used every day for a week, often short journeys,(e.g. 2 miles total), and then sit for 3-4 weeks at a time without being started. It also does longer journeys of 50-60 miles less frequently.

It sits in the street, so I can't put the battery on a trickle charge. I have a portable power pack to jump start it when it hasn't been used in a while.

I know these aren't good practices for keeping a car and battery in good condition, but my personal health is variable, so sometimes my poor old car gets neglected until I am going through a good period of health.

The battery was replaced with a new one in July '09.

Now to frame my question(s):

How long does it take for the battery to become fully charged from the alternator, either in minutes running stationary or in miles driven. Fully charged in the sense that it has enough power left to re-start the car within say 5-7 days?

I recall once jumping the car then going about 3/4 of a mile to the filling station. After putting fuel in and starting the car, it cranked slowly for a moment then fired up, which suggests the battery didn't have much power in it.

When I jumpstart it for use, and it hasn't been driven for a while I try to take it out on the open road and drive it up to speed for 5-6 miles out of town to give the battery a boost. Does this make any difference to simply letting it idle for 20-30 minutes to charge it up??

Answer 1

Depending on the type of battery you have it might self discharge between 10% and 40% per month. If you have a 600 ampere hour battery that discharges at 40% per month you would need to provide about 250 ampere hours to fully recharge it. If your car has a 100 amp alternator that amounts to about 2.5 hours to recharge the battery and that assumes your cars accessories did not use any power when it wasn't running and don't use any power when running. You probably need to run your car at least six hours per month to maintain the battery charge. Using a typical 12 amp battery charger you might need 48 hours to fully recharge your battery. These numbers are just very rough approximation.



The best solution for your situation would probably be to install an AGM battery (Absorbent Glass Mat). These are the batteries that discharge at less than10% per month compared to as much as 40% per month for the usual flooded cell car battery. From your description of your car usage the few extra dollars an AGM battery will cost will quickly be recovered from the gas saving of useless idling or driving and extended battery life.



Read the link for a quick tutorial about AGM batteries if you're not familiar with them. Virtually every major battery manufacturer has a line of AGM batteries for cars.

Answer 2

There are different factors that you need to look at.



First, is the battery a maintenance free type whereas you cannot open the individual cells to look in? Because I do not believe in maintenance free batteries. They have one green/red eye on ONE cell to tell you if the battery is charged or not. So the one cell is not going to tell you that.

Regular batteries have individual cell caps that you can open and look inside. Make sure that the fluid level comes to the top of the lead plates inside. Try to use distilled water to fill the cells with. This will prolong the life of the battery as regular tap water has minerals in it that can neutralize the acid inside. You can purchase a cheap battery acid tester at any local parts store. It will tell you what the specific gravity is on each cell and normally has a "good" or "no good" reading range on them for the person that is not very knowledgeable.

If you have one cell that is going bad it can drain down the whole battery's ability to hold a good charge and requires longer time for charging.

Check Your battery terminal connections and the cable wire crimped into them. These can build up corrosion that reduces the battery's effectiveness and also hinder in the alternators ability to charge the battery. You can also pick up a charge meter at your local shop to tell you what the charge voltage rate is. This is a good thing to have as most cars only have indicator lights on them instead of gauges anymore. The dash light will only come on when the alternator is no longer working.

Keep the tops of your battery clean. Corrosion coupled with grime/dirt on top of batteries can actually act as a path for the voltage to travel out of the battery and drain the battery down.

Use some common baking powder "Arm & Hammer" is best. Take a couple of teaspoons to a glass of water and mix it up well. Then pour it out over the battery, being careful not to get any inside the cells. Let it stand for a little while so it can neutralize any acid and corrosion and then simply wash off with hose water. Remember to be safe and wear eye protection and some common rubber gloves. Any acid splash can burn the skin badly and hurt your eye sight if it gets in your eye.



I would suggest that if you are not going to drive the vehicle for weeks on, that you at least go out and start it up and let it run for @ 15 minutes. This sould be plenty of time to allow the alternator to keep the battery charged up. Weather conditions can play into the factor though. Cold winter weather can reduce a battery's effectiveness quickly. So keep that in mind.



Also, with the electronic ignition on todays cars be very careful how you jump start. Take your negative ground and clamp it directly onto a good ground on the engine, then take the positive clamp and place it on the positive post on the battery. If not you run the risk of burning out delicate electronics in your vehicle.



Hope this all helps you. Good luck!

Answer 3

alternators charge very slowly, i would get a trickle charger and let it slowly charge it, but overtime it will kill the battery, basically buy a beefy one and drive it a bit more if you can even though the car isnt running there is still some components that are pulling a charge that is why it drains

Answer 4

No there isn't> 12.3 the battery is almost dead> But will run things till all voltage is gone> It going to take more charge than your giving it> to fully charge the battery> As the next day the battery will be even less charge than the day before>

Answer 5

let it idle 30 min. every 2 or 3 days.