Deep cycle battery in a car?

Here's a better idea; Find your charging system fuse and change it . You battery will subsequently be able to charge. Too bad you spent hundreds of dollars fixing what a $1 fuse would fix.

It won't help much, most people misunderstand the concept of a deep cycle battery. It has nothing to do with total capacity. It has thicker plates that won't be damaged by a deep discharge, but the result is they are more susceptible to being damaged by heat from high current loads. The thickness of the plates does not increase the total capacity. If a typical automotive battery is regularly discharged to 50% it will make the battery only last for months.

A deep cycle will discharge at the same rate as a conventional battery when used for the same purpose, but the high amperage starting requirements of the car may damage and shorten the ability of the deep cycle to be recharged.

Typically a deep cycle battery needs to be about 25% larger than a conventional battery to get the rating needed to not damage the battery when starting. That larger battery may not fit into the car.

The deep cycle will have the best voltage available right after a charge, so starting with a fully charged deep cycle will cause it the least damage. So charging it between every stop would make a deep cycle battery last longer than a conventional battery when used as you are suggesting.

But still not a good option, but if you already have a 12v deep cycle battery and no option to fix your car correctly a deep cycle would work better if you have one already that is larger than the original.

It's likely an easy fix for someone that knows what they're doing. Take it to a local independent shop and explain you don't have a lot of money, be nice and patient, most will help you out cheap.

Before you take it in check all the fuses and make sure the alternator belt is tight.

It would work, as a band aid. I drove a 69 Volvo 6 cylinder for 3 days before the new battery died. They installed a new + battery cable and it didn't have a wire going to the alternator. That was in daylight using no headlamps. You could probably run it two days then charge it.

On your problem though, is the alternator lamp illuminating on your dash with the key turned to on? If not, that bulb will cause the alternator to not charge the battery.

The bigger the capacity, the better. Just getting a D/C the same CCA will be of little advantage. It just can take a continuous load, like radio on all night..

I think your problem is something else. like fusible link/fuse/loose belt. Take it to the Zone and have them check it when running.

A deep cycle battery does not have more capacity than an equivalent car battery, it is just more forgiving of repeated deep discharges.

Because you have to get the charging system fixed very soon - even a deep cycle battery has its limits - you should focus on that. A mechanic should find the problem pretty quickly through actual troubleshooting, especially in a 1979 Mustang. I am not a mechanic, I'm an electronics/IT tech, but I could give you a good idea what is happening within 5 minutes and a solid diagnosis within 30 minutes of the time I touched it.

A deep cycle battery CANNOT be used in a car. See a very good mechanic to get your car fixed.

You need to have a certified technician check it out and make recommendations.