WIll my car's battery last long enough?

Question

Well I want to use my portable DVD player in my car so I want to know how long I will have to watch the movie before my car dies.

Now I can't leave my car running coz my car's too loud (after market pipes) so I'm wondering if my car's battery will last long enough to watch the movie. I will have the keys turned back in accessory mode to power the outlets. I had the battery replaced a few months ago so it's fairly new.

Oh and also what if I had the car stereo on to listen to the movie through an auxiliary port? How much time would I have there?

The battery that came with the player doesn't work so I can't charge it.

THANKS!!!!

Answer 1

The portable DVD player probably doesn't use much power so it should last all day.  The only way to be really sure is to hook a good accurate digital multimeter to the battery and watch the display on it while the DVD is playing inside and count the number of hours it takes to go from the fully charged resting voltage of 12.6-12.9 down to 12.00 which is 50% discharged.

I wouldn't do it very often though since unless you have a true deep cycle battery you will kill it with a few deep cycles from running accessories.  Common cheap starting batteries have lots of thin pasted lead plates for maximum lead to acid surface area contact so that they can provide the amps needed to crank the engine.  Deep cycle batteries have fewer plates that are either mostly solid or are a thick paste and each one is thicker for maximum active material and maximum amp hour capacity.  The problem with lead acid batteries is that when they are cycled (run down and recharged) the plates shed some material which falls to the bottom of the cells and becomes useless.  Starting batteries shed material much faster because the paste isn't very strong and after a few deep cycles the plates will either have nothing but the grid left or the paste that was shed will build up in the bottom of the cell until it bridges between 2 plates and shorts it out.