questions about a car's battery

[pyehac]

I have a 2004 Mazda3 and I forgot to turn off the interior light of the car for a bit more than 24 hours.

1) would have leaving the light on drain the battery to the point where I'll need to replace it?

2) I replaced the battery a couple of months ago. How can I check how much charge is left in the battery?

If it helps, I use the stereo every time I drive it (mostly 7 days a week) and it charges my iPod while I listen to music.

[BGM]

car batteries will 'last' for ages, by that i mean the life of them decharging and recharging

if you changed it a couple of months ago i wouldn't worry about it.

change the battery when it breaks (stops holding charge), it won't really hurt anything as you will only notice it has 'broken' when you come to start the car and, well... it won't :)

Edit:

re-reading your post, it seems to suggest you believe the capacitance of a car battery is fixed.

you do know that it charges itself up from the engine every time you drive yes?

this is why having things on like the aircon, radio, lights etc consume more fuel... because the battery is needing to be charged. just checking ;)

[MarkusDarkus]

No you shouldn't need to change the battery It's like a mobile phone battery. Just get a bump start and keep high revs for a while to re-charge it in a rush (Depends on how dead the battery is). Or you can get hold of a car battery charger. It's a box that goes between the wall socket and car battery.

[ceminess]

http://en.wikipedia.org/wiki/Car_battery - If you feel like reading how it works

basically, while you are driving your car, your alternator recharges your battery. As long as you can start your car, there should be no worry. If you are worried, then like MarkusDarkus suggested, sit for a few minutes after you first start your car, and rev your engine, or keep your radio, lights, ipod, ect. turn off while you drive (for like 10 min. or so).

Again, with it being a new battery. You should have nothing to worry about, one HUD light shouldn't drain your battery too much.

[rathefeare]

car batteries will 'last' for ages, by that i mean the life of them decharging and recharging

if you changed it a couple of months ago i wouldn't worry about it.

change the battery when it breaks (stops holding charge), it won't really hurt anything as you will only notice it has 'broken' when you come to start the car and, well... it won't :)

Edit:

re-reading your post, it seems to suggest you believe the capacitance of a car battery is fixed.

you do know that it charges itself up from the engine every time you drive yes?

this is why having things on like the aircon, radio, lights etc consume more fuel... because the battery is needing to be charged. just checking ;)

The aircon specifically the compressor is driven directly off the engine. The battery doesn't play a part there except the electric fan circulating the cool air. There is reduced fuel mileage and HP when the AC is on of course though. I doubt you would be able to see a difference in fuel mileage with the lights and radio though. I am sure there is some, but it is probably only detectable in a lab.

[BGM]

The aircon specifically the compressor is driven directly off the engine. The battery doesn't play a part there except the electric fan circulating the cool air. There is reduced fuel mileage and HP when the AC is on of course though. I doubt you would be able to see a difference in fuel mileage with the lights and radio though. I am sure there is some, but it is probably only detectable in a lab.

oh right, learn something every day..

as for the lights and radio, i still turn them off when my refill now light comes on, and i'm lost.. makes me feel less nervous, lol ;)

[robertwnielsen]

http://en.wikipedia.org/wiki/Car_battery - If you feel like reading how it works

basically, while you are driving your car, your alternator recharges your battery. As long as you can start your car, there should be no worry. If you are worried, then like MarkusDarkus suggested, sit for a few minutes after you first start your car, and rev your engine, or keep your radio, lights, ipod, ect. turn off while you drive (for like 10 min. or so).

Again, with it being a new battery. You should have nothing to worry about, one HUD light shouldn't drain your battery too much.

Ceminess,

It depends on which light it is - the way I read it, it sounds like the OP is referring to the overhead dome light...and leaving that on for 24 hours can definitely drain a battery to the point of needing a jump start/recharge (I know, because it happened to me!

Now, my battery was a little older when this happened....if the OP's is brand-new, he might be okay, like MarkusDarkus says, if he can start the car and allow the alternator to charge the engine for a few minutes without any accessories on, he should be fine.