How to check battery and altanator on most cars and trucks.

First anytime you charge a battery it gets warm your exciting the electron flow from the battery acid and forcing them back onto the plates. This Process produces heat during the electron flow and when you discharge the battery by cranking it over for to long you can actually warp the plates and burn the battery up. Also if it has a shorted plate and is not filled with water it could explode. So always add water to the full mark before charging the battery.

Now We need to discover what the problem is on the charging system or the battery if there is a problem, to do this you can clean the battery posts and terminals yourself it will save you time if you do it at home. Also use safety glass’s and rubber gloves Battery acid is very corrosive and can absorb into your skin and can blind you or can be absorbed into your skin and if enough of it gets absorbed this could cause brain aneurysms. And blindness. Remove the terminals and with a sharp knife peel back about a half inch of rubber from the terminal on the negative and positive cables now twist the cable by the terminal and hold the cable with the other hand do you see any blue or green or white corrosion on the cable? If yes you will want to replace the cable ends if the cable is long enough cut the ends off and buy two new battery post terminals at any parts store. After you have done this Charge the battery up first. Then drive to the nearest Auto-zone store and have the test the battery do a load test on the battery the battery should read 12.5 volts dc if not have them do a quick charge to bring it up to 12.5 to 13.5 volts. Once it is charged then they will do a load test on the battery depending on the amperage rating of the battery yours will most likely be an 800-ampere hour rated battery. They will input this information into the load tester and put the battery under load by turning a switch and this will do a load test threw a carbon resistor that can draw the battery down at half the rating of the battery (Rough Estimate) they will do the load test for 30 seconds if the battery drops below 9.5 volts while and after they turn the switch off you have a bad battery if it maintains 9.5 and recovers to 12.5 volts then the battery is ok. Now you test Alternator output while you are there to do this they will put the voltmeter on the battery and have you start the car and rev up the engine to 900 RPMS at this time the alternator should be putting out at least 13.5 volts and no more than 14.5 volts. Next you will turn the head lights on high beam and turn on the A/C and turn the Fan on High and read the voltage if it stays at least 13.5 you can assume the Alternator is ok if it drops below 12.5 volts with everything on at 900 RPMS then your alternator is defective or the regulator is defective. If everything checks out ok you will need to have a test light and a voltmeter to test the electrical system. I am going to give you enough information for you to know if you need to take it to a shop.
Once you get home pull the positive cable off the battery with your gloves on and all accessories off no lights on and the door closed take the test light on the end of the battery post then the other end of the test light to the positive cable, you should have no light or at most a very dim light if you have a stereo or power amp that comes on with the radio on. If you have a bright light then you have something making contact, so remove any overhead light bulbs glove box bulbs or any inside marker or safety lights. Check the light again, is the light off? If yes you have narrowed it down to one of the items you have removed. Start putting the items back in till the light comes back on when the light comes on you have found the circuit that is making contact that should not be, it can be caused by a bad bulb or the end of the bulb could be shorted, this happens when the bulb is old and the ends flatten out then ends are soft so vibrating can wear them down they should be rounded at the end of the bulbs.

If the light is still on remove the fuse box cover and start removing fuses one at a time as you remove the fuses watch the light once you see the light go out you have found the circuit that is on and should not be. With all of this information you can take it to a mechanic to have that circuit checked for shorts or you can tell me what fuse it is and I can give you further instructions on testing for a short. There are many things that can cause this so once you have done this in order I have put here you have done the testing in a way that eliminates the battery, battery posts and alt. And battery condition, this saves you about $65.00 this you can do yourself if you have a slight clue as how to use a wrench and a test light. One other thing when you disconnect the battery for more than a minute you will lose all information in your computer and all radio settings and seat and mirror setting if you have these acceories. It will have to learn how to shift again and set timing so it may drive a little different for a couple of days, this is normal for most newer cars with computers. I am including this so you don’t waste your time and the mechanics time when it acts funny for a couple of days. Some drivers notice a difference in what the car does and some people don’t. The more you can detect and describe the problem more the more help you are to the mechanic, this saves you money. Good Luck and Hope this helps thanks for using fixya.