Changing batteries on 2007 Sea Ray Sundeck 240

Ed Gallo

Ed Gallo

New Member
Aug 28, 2020
10
Boat Info
2007 Sea Ray Sundeck 240
Engines
Mercruiser 350 MPI Bravo 3
I am replacing the batteries on my 2007 Sea Ray Sundeck 240. Should 1 battery be a "starting" battery and the other be a "deep cycle"? Can both be "starting" batteries?
 
No you want both deep cycle... starting battery is not necessary plus you want power to last as long as possible
 
I don't think deep cycle batteries are meant to be used for high amperage draws like starting the engine.

I have 2 starting batteries and never have an issue
 
100% disagree with a 350 MAG....

I have had 5 240 Sundecks and 2 260 Sundecks all with 350MAGs all over 15 years and all had 2 deep cycle batteries..... my current boat has 2 deep cycle batteries for each engine and double as house batteries.....

If you anchor out at all...you want deep cycle
 
Last edited:
We have deep cycle batteries to start our 454s. Two group 27 per engine. On jetboat that has a 350 we have two group 24 deep cycle. All the batteries work well. Deep cycle batteries have thicker plates and take the pounding better. Never had any problems with the jetboat that is more like your boat. We get our batteries at Costco.
 
Don’t confuse true deep cycle with dual purpose. A true dedicated deep cycle battery will not have enough CCA to turn over a boat motor. A dual purpose (marketed as deep cycle) is designed for longer amp hour life while maintaining the CCA required for starting. Almost all batteries marketed today as deep cycle are actually dual purpose, and perfect for the OPs boat.
 
Thank you all for the responses. I replaced one of the batteries with a "starting" battery and I assume the 2nd battery is the dual purpose (deep cycle) battery. Do you usually change both batteries even if one of the batteries is still working properly? I've had the boat for 5 years - same batteries came with used boat. I noticed that even with the new "starting" battery, the engine is slow to "turn over". I am in the Northeast and its starting to get cold here. In the past, the boat would immediately turn over and start...now it seems like its struggling. Not sure if that's from the cold weather, which leads me to my next question regarding the battery switch. I always start and run the boat on "both" and if I'm out on a hook and playing some music, I switch it to 1 or 2. Is this the proper way to run the battery? Also, can I keep one battery as a "starter" battery and use a "dual purpose" battery as the second battery? I saw some posts that the alternator will charge both batteries even if you don't have the switch in the "both" position. Is this the case with a 2007 sea ray? I was running on "both" because I had been told that the alternator would only charge the battery of the selected position??
 
Ed Gallo said:
Thank you all for the responses. I replaced one of the batteries with a "starting" battery and I assume the 2nd battery is the dual purpose (deep cycle) battery. Do you usually change both batteries even if one of the batteries is still working properly? I've had the boat for 5 years - same batteries came with used boat. I noticed that even with the new "starting" battery, the engine is slow to "turn over". I am in the Northeast and its starting to get cold here. In the past, the boat would immediately turn over and start...now it seems like its struggling. Not sure if that's from the cold weather, which leads me to my next question regarding the battery switch. I always start and run the boat on "both" and if I'm out on a hook and playing some music, I switch it to 1 or 2. Is this the proper way to run the battery? Also, can I keep one battery as a "starter" battery and use a "dual purpose" battery as the second battery? I saw some posts that the alternator will charge both batteries even if you don't have the switch in the "both" position. Is this the case with a 2007 sea ray? I was running on "both" because I had been told that the alternator would only charge the battery of the selected position??
Click to expand...
Let me offer up some answers, and I am sure others will have more to add.
It is fine to use one starting and one deep cycle as long as you remember to switch them for running and on the hook. For the boat you have, two group 27 or 31 dual purpose would be perfect, just get high MCA (over 800) and high reserve (over 160) and you would be set.
Starting and running on both is ok but not ideal. If one battery goes bad, it can drag down the other and you might not know it until you try to start.
If you have a VSR or ACR then both batteries would charge regardless of switch position. My guess is your boat does not have one, so it likely only charges the battery selected on the switch.
My position - SR did not wire this size boat with engine and house separated like it should be, at least I have not seen a factory one wired that way. They wire it as primary and back up batteries. Therefore, I would get two Sams club group 31 agm batteries if they fit in your set up, and alternate which one I used each trip. Your load would take days to draw down that size battery so no need to switch while on the hook.
 
I run one of each, deep cycle and starting. I only run one battery at a time and switch between the two. 1 on odd numbered days, 2 on even. Running on both can damage a good batt. if other has a bad cell. I've not had a problem in many years.
 
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