Starting vs dual purpose

On rainy this weekend. After being anchored for several hours with 2 12” helixs and a 9” garmin running, motor wouldn’t crank. 2013 90hp 4stroke merc. tiller. I have a group 24 interstate cranking battery. I knew it was getting tired so not a big surprise. Battery runs cranking, graphs, pumps and power steering. I’ll have to get actual dimensions but not sure if a group 27 will fit. Don’t really have room to add another battery due to power steering pump.
Would I be better off with a dual purpose battery vs a cranking battery?
Thanks.

I don’t know which is better. Have ran both with no problems but never ran that many graphs etc.
On battery size check and see if a 27 group will fit. Many times if there is room for a 27 you can make a 29 group fit. Usually there is only about 1/8 to 1/4 inch different between a 27 and a 29.

I only have a group 24 now. Hoping to get a group 27 to fit.

I cut the ends off of my battery tray so I could put a 29 dual purpose in mine. These big graphs use a lot of juice. Bigger is better!

I would have no problem doing that, except the door on the compartment isn’t big enough. Had to pull one of my group 29 deep cycles from the front to start the main motor. It wasn’t even close to fitting through the compartment opening.

I just upgraded to a group 27 last year with a higher reserve, no issues now with two units running all day

To answer your question on the cranking vs dual purpose. The dual will have better run time for the electronics and is fine to have hooked to the charging system from what I have been told the charge rate is no high enough to overcharge them. I have even ran a straight deep cycle in the starting position before and it works fine. Not sure on some of the new motors with higher amp charging systems, but if I were you I would swap it out with a dual purpose of a quality brand. I run either Interstate or Napa Legend.

Well my current group 24 interstate with 1000 cca and 135 reserve tested out good on 2 different testers at Napa and a third at Auto Value yesterday. Any bigger battery either had was to long to get in the top of the compartment. So I might be cutting the aluminum lip out of the compartment to make room for a larger battery. Hate to do it but to get a bigger reserve I’d have to go deep cycle, but then cca drop significantly it seems. Unless anyone has a different option.
Picture of opening I have to work with.

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Red Eye wrote:

On rainy this weekend. After being anchored for several hours with 2 12” helixs and a 9” garmin running, motor wouldn’t crank. 2013 90hp 4stroke merc. tiller. I have a group 24 interstate cranking battery. I knew it was getting tired so not a big surprise. Battery runs cranking, graphs, pumps and power steering. I’ll have to get actual dimensions but not sure if a group 27 will fit. Don’t really have room to add another battery due to power steering pump.
Would I be better off with a dual purpose battery vs a cranking battery?
Thanks.

If you’re going to be anchored for several hours, maybe shut off a graph or two or three? I run a marine deep cycle for my starting battery because of big graphs. It’s a 29 series though but if I recall it actually had more cca than my interstate 24 starting battery it replaced.

Might you have room for a smaller “vexilar” type of battery or two to run directly to one or two of the units?

Or perhaps if you are going to be sitting still for that long; start your big motor and let it idle for 10 minutes every hour or so?

Cranking batteries are designed to be used in this manner. They run best to power graphs, pumps, lights, and an electric start outboard. Dual purpose will work but if you don’t intend to use it for anything else I would stick with the cranker. As others have mentioned, running several items on them for a long period of time, especially on a 24 series battery, could drain it. Make sure its a good battery and fully charged before you use it.

A deep cycle battery is not designed to run those items. They are for a trolling or electric motor. Avoid using a deep cycle for those items if you are able to. A deep cycle used for a trolling motor could be used in a pinch to fire up the outboard. I have done it. A portable power pack like a NOCO works too.

You could upgrade to an AGM or even a lithium battery but the price tag is higher than a standard battery like an interstate. I believe they come with a longer warranty though too. There’s definitely a trade off. Some people get good life span out of a standard battery and some are willing to pay for the potential extra life of an AGM or lithium.

I have ONLY ran deep cycle in my time owning and operating a boat.
Currently have 2x 31 powering the graphs and motor and another 2 powering the trolling motor.

1x 24 to run those electronics isn’t enough. Find room, make room, buy bigger.

This is taken directly from Odyssey’s website on recommended battery usage based on each type.

Types of Marine Battery Applications

Deep Cycle
A boat’s trolling motor relies on deep cycle batteries. These batteries are the marathon runners of the boat’s storage system, as they power the electrical loads on the boat when no charge source (shore power charger, engine alternator, wind generator or solar panel) is available. They are intended to discharge energy over long periods of time, using approximately 50-80 percent of their capacity, and are able to recover completely afterwards. They are built with thicker plates than starting batteries and are significantly heavier than a starting battery of similar dimensions.

Starting
Also known as a cranking battery, a starting battery powers the starter motor, enabling the engine in the boat to start. Starting batteries are easily depleted and rely on an engine’s alternator to restore the charge. They house negatively and positively charged plates that are separated by insulation. One of the main differences between a starting battery and a deep cycle battery is the thickness and number of charged plates. Along with engine starts, starting batteries are commonly used for bilge pumps, navigation, courtesy lights, aerators and general marine electronics.

Dual Purpose
Simply put, dual purpose marine batteries can perform the function of both traditional deep cycle and starting batteries. With larger, thicker plates than starting batteries, dual purpose batteries are ideal for tolerating deep discharges that would ruin a typical starting battery. This class of batteries contains a small amount of liquid, just enough to moisten the internal plates so nothing can break or leak out. This design makes these types of batteries durable, stable and able to start the engine while powering the electronics over the course of a full day on the water.

I will second the comment, if your anchored for several hours why do you have 3 graphs running? You can put a bigger battery in that 11″ opening just have to angle the battery going in.

This topic seems to come up from time to time and there were guys that I assume are still here know far more about the makeups of batteries and what is best to use under each application and I recall them say that a deep cycle for a cranking battery is fine because of the extended load being consumed by the larger electronics, constant running bilge pumps etc. I know my boat came with a 24 cranking battery which quickly was tossed for a dual purpose 27 which has now been upgraded to 2 29 batteries in parallel. I dont have a load that the OP does as mine are all 7 inch displays, but so far no issues for me.
Also keep a set of jumper cables in your boat to run from trolling motor batteries and a jump pack so you dont get stranded.

bigcrappie wrote:

I will second the comment, if your anchored for several hours why do you have 3 graphs running? You can put a bigger battery in that 11″ opening just have to angle the battery going in.

Ya I probably should have shut down at least one graph. Hind sight. As for getting a bigger battery in the hole by angling it. Not gonna happen with the steering pump in the same compartment. Believe me I tried.

I am upping my graphs to 2 12 inch HDS Lives with active target this year and am adding aLithium 24AH hour “House” battery, according to everything I read there is more almost double the usable AH in a LIFEPO4 battery before the voltage drops too low

Well I found a Deka 27m6. 840 CCA and 182 reserve capacity. Hopefully it helps. It still wouldn’t fit in the compartment so had to do some modification. First pic is with new battery. Second is before with old battery.

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Red Eye wrote:

I would have no problem doing that, except the door on the compartment isn’t big enough. Had to pull one of my group 29 deep cycles from the front to start the main motor. It wasn’t even close to fitting through the compartment opening.

Red Eye –

This is the exact reason I carry jumper cables in my boat so it’s not a big deal if (typically when) this happens. I bought 2 cheaper sets and combined them together to accommodate the length needed to reach from trolling motor batteries in the front to the starting battery in the back.

Another option is to have a second battery in battery case mounted to your floor outside the compartment (out of the way if possible) and run two batteries in parallel. Good luck with your new battery!

I’d seriously just buy a NOCO GB40 and not mess around with an extra battery or jumper cables. $100 is cheap insurance, and you can use it to jump other vehicles, too.

Yes normally always have jumper cables in the boat but it was the first trip of the year.

Just get a deepcycle AGM. It is best for your electronics. It will last the longest. They have more than enough to CCA start the big motor. Mine have 1150 CCA. I have the Northstar Group 31 AGMs. One battery runs all my electronics and boat equipment. Stereo with amp and powred sub. 3 Helix 12s. Baitwell, livewell and lights. Never have not been able to start my big motor

Consider a Noco jumper gp70. It will jump your dead battery in both boat and truck AND power your electronics when ice fishing.

Power steering in a boat? Dang Red Eye!

Sylvan that Noco looks sweet, but a boat needs more than a jump with EFI, do you keep the unit on until you get back to the launch?

After the motor is started, won’t the motor’s charging system recharge the system enough to power itself back to the boat launch? I’d think it should unless something is wrong with the charging system.

Most outboards will run without the battery, once you get them started.

It is not recommended to disconnect it after it is started, it is hard on the charging circuits.

But like your car, the stator/alternator with support the motor operations.

One nice thing I had my guy rig on my boat is a jumper switch. This allows me to jump the crank battery off the TM batteries by just flipping a switch. No jumper cables or any of that. This has saved me a couple times after long days on the water and only takes a second to flip the switch then the engine is up and running.

I just saw this thread and wanted to reply. In full disclosure I didn’t read through all the comments.

All I did is see people saying not to use a deep cycle battery for a starting. Completely false. I talked to a battery manufacturer and they will work just fine for starting an outboard. And will run all of your electronics equally well. With that said I fully endorse using the largest deep-cycle you can fit for your starting and electronics.

Joe Scegura wrote:

I just saw this thread and wanted to reply. In full disclosure I didn’t read through all the comments.

All I did is see people saying not to use a deep cycle battery for a starting. Completely false. I talked to a battery manufacturer and they will work just fine for starting an outboard. And will run all of your electronics equally well. With that said I fully endorse using the largest deep-cycle you can fit for your starting and electronics.

Correct Joe