battery light

First make sure that you don't have a glove box, ashtray, or underhood light on constantly or something like that. Do you have an aftermarket sound system? Sometimes a sound system will still use power when the car's shut oiff. Also tell us how you are checking batteries and alternators for failure so there's more to go on. Make sure that your battery cables are in good shape, no bulges with corrosion, etc. and that the battery and terminal clamp surfaces are bright clean and tight on the battery posts. If you want to check for "ignition -off draw" with the key off, and safety goggles on, disconnect the negative battery terminal and observe if there's a spark when you touch the cable to the battery terminal. You can't do this in sun, you need to be in the shade to see. If there's a big spark, you have some device drawing current when the car's off and that will ruin a battery.. A small spark is normal. If you have a meter, you can measure the draw. Any more than about 15 milliamps oi too much and will run your battery down.