First off, while you can never use a starting battery for deep cycling (it will kill the battery in short time), you can always use a deep cycle for starting.
Second, here are the specs from Optima's website at:
http://www.optimabatteries.com/products/pdf/TF.pdf
and
http://www.optimabatteries.com/products/pdf/34M.pdf
34M starting battery: 12.8V, 50 AH, 104 minutes reserve, 800 CCA, 980 MCA
Troll Fury deep cycle: 13.2V, 110 AH, 240 minutes reserve, 1300 CCA, 1740 MCA
The Troll Fury puts out significantly more CCA/MCA (starting power) while having more than double the reserve capacity and AH as well as a higher voltage. So the argument that deep cycles don't put out enought start energy is moot.
Also, from Optima's FAQ at
http://www.optimabatteries.com/faq.asp :
"What is the difference between your deep cycle and starter battery?"
"The OPTIMA deep cycle battery utilizes a different chemistry for the active paste material on the plates, and a slightly stronger acid. This chemistry changes allows for a much longer life in cycling applications, with only a slight reduction in power."
This slight reduction in power is more than made up for in the Troll Fury by virtue of the fact it is actually 2 batteries in a single case...2 slightly weaker batteries is stronger than one slightly stronger battery.
From the same FAQ:
"When should I use a Deep Cycle OPTIMA as a Starting battery?"
"Deep Cycle" batteries are designed for applications that require deep, repetitive amperage drain, like trolling motors, golf carts, and electric wheelchairs, or RV house power sources. However, there are other applications, called "Heavy Cycling" or "High Cycling", when a Deep Cycle OPTIMA can successfully replace a starting battery to provide longer life and better performance."
"In heavy cycling or high cycling applications, a vehicle will pull unusually high amperage levels from the starting battery due to extra accessories or limited alternator capacity. Public safety professionals, such as police, fire, and ambulance fleet managers often find that traditional starting batteries cannot provide adequate life and performance due to heavy cycling. This is an excellent opportunity to provide your customer with longer life and better performance by using an OPTIMA Deep Cycle battery in this type of application."
Heavy cycling is basically when your alternator can't keep up with the loads demanded of the battery...the battery has to make up for it...like running your livewell, electronics, etc while loping along trolling (and consequently not putting out full rated power from the alternator). This is compounded by the wimpy alternators most marine engines come with.
[b]"To provide the customer the best OPTIMA solution, it is, necessary to consider both the application and the charging system before recommending the correct OPTIMA. For example, if your customer has a Ford Expedition with an after-market alarm system, which OPTIMA would you recommend?
If the customer drives the car every day, the Red Top would be the correct choice, since the amperage drain will be nominal and the battery would be recharged on a daily basis. However, if the customer stores the vehicle for a long period of time with the alarm system engaged, you should recommend the OPTIMA Yellow Top, since the amperage drain over several weeks would damage a Red Top and reduce its life."
Again, the second case is much like a boat...not used for a week or more at a time, slow load drainage from a cycling bilge pump, etc. If all of this sounds like how you use your batteries, then deep cycle is the way to go.
I personally have two banks of batteries and two battery switches (A and B). I can run battery 1, 2, or Both on either switch. The switches determine which loads are carried by which battery...Switch A is for Helm loads (starting, engine instrumentation, accessories such as the livewell, fish box macerator, washdown, engine hatch, nav lights, search light, etc). Switch B is for House loads (fridge, cabin lights, head, stereo, water pressure, etc) as well as electronics (to prevent spiking when starting the engine, I ensure both switches are not on the same battery bank).
Running the engine (or the converter when tied to shore power) charges both batteries through an isolator, keeping both batteries fully charged (I also replaced the wimpy 55 amp alternator with a 130 amp alternator). When I take the boat out, I generally start the engine with each switch on a different bank (and I alternate whcih bank every trip). When the engine is running, both banks remain charged. If I stop the engine for an extended period (like at anchor or drifting over a chum slick, etc), I switch the helm switch to the opposite bank (both switches on the same bank). This ensures there is a fully charged battery to start up later.
Hope this helps you both in dispelling myths about deep cycle batteries as starting batteries and in setting up your DC system to ensure clean power for electronics as well as an always ready starting battery.
BTW, the article BW23 suggests reading at
http://www.yachtsurvey.com/boat_battery_basics.htm suggests the following:
"When deep cycle batteries are used in boats, it is necessary to have considerably greater amperage than that required by the engine starter. This is almost never a problem since these batteries are used in banks of more than one battery per bank. When you get up to sizes like 4D and 8, 125 & 250 AH respectively, even a single battery is more than adequate because the amperage is so high." "Further, if you're going offshore where there may be high demand on bilge pumps, BEWARE that cheap automotive batteries aren't going to run our pumps for very long, particularly after engine failure. Offshore operators should use higher capacity deep-cycle batteries."
One last thing about Optima Troll Fury batteries...they are completely sealed (they can't leak, the electrolyte can't boil off) and they have an 18 month no depreciation repolacement warranty with an additonal 18 months prorated replacement warranty
Harr
[This message was edited by Harry Brosofsky on 04-15-03 at 01:28 PM.]
[This message was edited by Harry Brosofsky on 04-15-03 at 01:30 PM.]
Battery suggestion needed for offshore boat 
