Well its time. I bought this thing used and have been using the battery it came with. Its an Autocraft Marine 27DC Deep Cycle (it was used for starting and everything). Its about had it.

I have a battery switch but only one hooked up to it. I figured I should have a Starting battery and a Deep Cycle. The motor is a 5.0 Volvo Penta (Chevy 305) carbed. Is 500 CCA enough? I thought it only needed 375 but I always try to double the min.

Say a 24 series Marine Staring battery and a 29 series Deep Cycle Marine battery to power stereo, depth  finder and water pump? Is a 29 series ok to use for starts on occasion if say the main starting battery failed? When not in use its on a solar trickle charger. Should I go with two 29 series Marine / Deep Cycles instead ?

Just replaced one of my Walmart group 29s yesterday after 8 years.  I have 4 Walmart deep cycle batteries in my camper and 3 boats and have never had a bad one after quite a few years using them.  Hard to beat for $85 with a no question asked return policy just about anywhere.  For emergency starting a Gp 29 is fine as it has nearly 900cca but the charging system on the engine is not designed for deep cycle batteries and can ruin one quickly.  I always use large regular automotive type batteries for the cranking side and they do fine running most other accessories that aren't huge draws.

I agree with above post as far a deep cycle batteries are concerned. A typical alternator will either ruin the battery or the alternator over time. Buy two of the largest group size that will fit in the battery boxes/trays.
The higher the A/hr and cranking amps the better.
On another related note, don't switch the battery switch while the engine is running. This can hurt the alternator's regulator and other electronic devices on board.
What I recommend to boaters is to put the switch on "ALL" to get the boat started and to your destination like the beach etc.. This gives maximum amp delivery and allows the batts to charge en-route to the destination.  When you arrive at the destination, with engine stopped, switch to batt "2" to run the stereo and accessories while beached/anchored. This will prevent you from running both batteries down and un-able to start the engine.

One last note. The alternator will not charge a dead battery for long. Boat alternators aren't that powerful (amp wise) and will run at max output trying to charge a dead battery. This WILL overheat the output terminal on the alternator and ruin it. Ask me how many marine alternators I've changed due to this.

thanks. Going to go ahead and get the gp  24 starting and the 29 deep cycle. I need to get some cabling and set up the second battery to the switch. I need to study up