batteries

every battery is rated for CCA (cold cranking amps) .. as long as your batterie is rated higher in CCR than your starter it is ok .. most deep cycle batteries have less CCR than equivalent (in Ah) cranking batteries .. if you stress the deep cycle with too much cranking and run it at its limits all the time it will suffer .. with enough reserve in CCR a deep cycle should be fine .. I have a deep cycle marine batterie (AGM) in my boat and use it for cranking (V8 5.0 MPI) .. no problem ..
have fun
gmd

I would not they are too ruddy expensive to start with (no pun intended) they are not designed to be cranked.
cheer's Bob.

In an emergency - yes. Otherwise no, as they are not designed for high current draw.

If you haven't already got a battery by a hybrid version which allows for both CCA and Deep cycle use, such as the Optima Blue and Yellow top AGM's. Otherwise occassional starting of the battery won't hurt it.

Many so called experts will tell you no way Ron but in reality YES they will work fine & I agree with what GMD is saying as pretty spot on.
If you were to use a standard NZ70 sized 80AH deep cycle wet cell batt to start a diesel for example I'd suggest you may have some longevity issues, but fit a suitably rated batt they will last for years.
I did away with my starting batt altogether opting for twin 115AH deep Cycle Trojans wired in parrallel. Being large good quality batteries they not only start the car far better than before, they are now 3 & 1/2 years old with no sign of any problems. The Vic Police apparently had some of their 4by's wired up the same to run some high power usage assesories in the field.
The reason I went this way was to get enough power (230ah) to run lights & fridge for 3+ days in one spot & still be able to start the car without the need to fit an expensive isolator, generator or solar panel. The bonus is that as both batteries are the same size, construction & are never discharged below 35%, they should last conciderably longer than many other systems. The only down side I've seen is that I need to keep a close eye on the electrolite level as it does need topping up a few times a year.
Another intallation I've done over 4 years ago was to wire an 85AH deep cycle together in parrallel with an Excide Extreme & he's had no issues starting off it either.
Cheers Craig.................