Marine starting battery – Deep cycle or cranking?

Guys,

Think I’ll be replacing my starting battery soon. It currently powers all the electronics and starts a 75 hp Mercury 4-stroke. It’s now a Group 24 Interstate. I was just going to put another 24 in, or maybe even a 27. However, in ‘researching’ past threads here on IDO, I see a lot of guys recommending deep cycle battery as your starting battery. I can probably get a 27 deep cycle into the cranking spot, so…I might consider that if that’s still the current thinking.

I should say, I’ve never put my cranking/starting battery on a charger (my trolling motor batteries are) other than the beginning of the year/end of the year – and once or twice during year – and they’ve always lasted years without issue. So not sure if that ‘habit’ would influence deep cycle vs. cranking choice.

Check your battery tray. I attempted to switch to a 27 for my starting battery once and found it wouldn’t fit in my battery tray. Like you, I have run a 24 for a dozen years with no issues using it as a starter and powering my downriggers.

Deep. It will have much much more than enough cca to start your motor without damage.

For a longer lasting battery, having it hooked up to a charger may get a few more years out of your battery. The lower the charge on a battery the more corrosion occurs to your plates in the battery. Keeping it charged will help to preserve the plates.

I bought this for my starting battery when one bank in my 4 bank Minnkota charger died. Works great.

NOCO Genius G3500 6V/12V 3.5 Amp Battery Charger and Maintainer https://www.amazon.com/dp/B004LWVEKS/ref=cm_sw_r_cp_api_i_bcodDb8DJ6ZV1

I use the bolt on terminals so I don’t have to attach the alligator clips every time I plug it in.

If nothing is wrong with the setup you have just duplicate it.

When I repowered I ended up having to ditch my deep cycle because it did not have enough cca. It was ok tell late fall/winter.

For a 75 of that vintage you can probably get away with either, just go as big as you can. Extra power is never a bad thing! For people who recommend deep cycles for everyone that’s not always a good thing. I work on many large outboards with digital throttle and shift and multiple modules in the system. I’ve seen where deep cycles cause very frustrating voltage issues such as modules turning on and off while the engine is being started. In all of those cases the only thing that made the system work correctly was installing the proper starting battery.

Just a friendly warning for the people reading this, and think they’re going to throw a deep cycle battery on a Verado for example. Engine manufacturers usually have a reason for specifying starting batteries in the owners manual. Outboards, and boats for that matter, are continuing to become more and more voltage sensitive. If having enough juice for your electronics and starting your engine when you want to go home is a concern do yourself a favor, and find a spot for an extra battery and install a isolator to charge both batteries.

Thanks guys. Good info/input. And yes, I better double check my battery tray size. Sure seems like I could get a 27 in there, but I’ll double check.

Still not sure on deep cycle vs. cranking for starter battery. I do fish late into the fall.

Hillhiker….saw your post right after I sent mine. Thanks for the input/info. Just to clarify, I’m running a 2009, 4-stroke 75 horse Merc “big tiller” for my outboard. I don’t know if that’s too ‘modern’ or not – in regard to your vintage point.

hillhiker wrote:

For a 75 of that vintage you can probably get away with either, just go as big as you can. Extra power is never a bad thing! For people who recommend deep cycles for everyone that’s not always a good thing. I work on many large outboards with digital throttle and shift and multiple modules in the system. I’ve seen where deep cycles cause very frustrating voltage issues such as modules turning on and off while the engine is being started. In all of those cases the only thing that made the system work correctly was installing the proper starting battery.

Just a friendly warning for the people reading this, and think they’re going to throw a deep cycle battery on a Verado for example. Engine manufacturers usually have a reason for specifying starting batteries in the owners manual. Outboards, and boats for that matter, are continuing to become more and more voltage sensitive. If having enough juice for your electronics and starting your engine when you want to go home is a concern do yourself a favor, and find a spot for an extra battery and install a isolator to charge both batteries.

Do you have any examples of situations where a deep cycle rated for starting and rated to the proper cca had issues starting a motor?

I agree with pairing the motor with a battery that meets the specifications but I’d like to understand how a deep cycle battery rated to spec would cause problems. Is it possible that the battery is simply shot?

Just an FYI. The interstate group 27 & 29 are both rated for starting applications. I’d have to assume that other bargain viands are not.

I’ve always ran deep cycles.
Current boat has two deep cycle 29’s in parallel for the motor and electronics.

Lots of electronics to run…a more regular draw than occasional starts.

Starts the motor in July @95° same as it does -5° in January.

Sure they are rated for starting does it mean they have enough current while maintaining voltage to do it effectively, on some engines yes. On engines that pull a lot of power turning the starter, powering up the engine ECM and a helm module, while firing injectors and spark plugs does require a lot of power. Some of those ECU/modules require 10.5+ volts to keep everything firing like it should, and in some cases the module will completely shut off when you get below that point.

The two most recent things I’ve dealt with were both related to voltage drop when the engine was cranking and specifically the start of the crank cycle when the motor draws it’s inrush current. The first boat the voltage was dropping below 10 volts while starting which was causing the engine ECM to shut off. The ECM would not recover fast enough and the engine would quit trying to start. The second was on a joystick boat, same type of issue though. When cranking the STBD engine the helm module shut off. If that isn’t up and talking the system will not start the engine. In both cases the battery tested good and both were right at 12.4V when checked with a meter. We installed cranking batteries and the voltage never dropped much below 11V and the system worked perfectly. Not saying this will happen every time you use a deep cycle, but electronics are very sensitive to voltage. When you are applying the huge amp draws to a deep cycle, like a starter does, it just seems like you see a larger voltage drop.

Go ahead and install what you want, but one of the main things I deal with on boats is voltage issues. It’s right up there with fuel problems. Think of it as fishing rods. One rod will do lots of stuff good, but most of the people on this site have multiple rods all for specific applications like trolling or jigging because those specific rods don’t just do a good job, they do a great job. I know in my boat there are 3 medium powers sitting next to me and they all have a specific purpose.

Now it’s time to hook the boat up and go fishing. Have a good weekend everyone!

Deep cycle batteries may work but they aren’t actually designed for use as starting batteries. Deep Cycle batteries provide a greater reserve capacity, but cannot deliver as many peak CCA’s (cold cranking amps) as starting batteries. Starting Batteries are made to provide high power for higher amp, more frequent short draws, and limited long term discharge.

If the setup you’re running works, don’t change it. I run a hds 9 and hook 7 on my cranking battery and I’ve run 4 hours without an issue starting. And I’m running a 60 horse merc

Here is a battery manufacturer’s chart for outboard CCA (cold cranking amps) requirements.

http://www.dekabatteries.com/assets/base/0406MarineApplicationslayout.pdf

they recommend 380 CCA for your outboard.

A group 24 starting battery has about 600 CCA and deep cycle battery has about 500 CCA. Based on specs either would work just fine.

A group 27 interstate deep cycle battery has 600 CCA so it is about the same starting capacity as a group 24 starting battery.

fish on ……

If it’s specifically just to start your motor, then go starting battery. if not, go deep cycle.