Thread: Deep Cycle vs Starting Batteries

My cranking battery runs down while fishing. I have a 24 Interstate to crank my Mercury 60, run depth finders and live well. After a day of fishing the motor won't crank. I thought my radio was killing it so I disconnected it and it still happens. If I don't run the live well it will crank.
I am going to a group 29 battery, all I have room for. Would a deep cycle be the best to keep the electronics and live well going and still be OK to crank with, since it is only a 60 hp.

Yes

A deep cycle is specifically for a "deep discharge" over and over again like you are describing. A starting battery is not meant to be deeply discharged over and over again; if you deep discharge a cranking battery over and over again it simply will not last very long.

Yes, go with the deep cycle as that's what I use with my 40 hp and livewell, lights, radio, and depth finders. I have a group 29, Everstart Marine, gives me 4 good years before it starts showing it's age....for $100 it's a bargain when you look at it as $25/year.

Using a deep cycle battery can interfere with your charging system and the starting system. Deep cycle batteries have thin lead plates that are meant to put out a very low
amperage over a long period of time like troling motors do. When you use one to start your motor, it pulls way too much amperage and creates heat in your starter, battery and in the wiring harness that will eventually lead to premature failure in one or all. Also a motor, like yours, with a stator and rectifier charging system are not meant to charge deep cycle batteries. The rectifier is a series of diodes (one way check valve for electricity) and resistors. The rectifier usually lets the battery over charge and causes its self to overheat and short to ground. I have a motor just like yours in my shop right now. I can text pictures if you would like to see what happens when a deep cycle is used for cranking. I recommend fixing the battery drain and switching to an Interstate 24M-XHD before you wind up spending a lot of money in repairs.

Originally Posted by Bullet101

Using a deep cycle battery can interfere with your charging system and the starting system. Deep cycle batteries have thin lead plates that are meant to put out a very low
amperage over a long period of time like troling motors do. When you use one to start your motor, it pulls way too much amperage and creates heat in your starter, battery and in the wiring harness that will eventually lead to premature failure in one or all. Also a motor, like yours, with a stator and rectifier charging system are not meant to charge deep cycle batteries. The rectifier is a series of diodes (one way check valve for electricity) and resistors. The rectifier usually lets the battery over charge and causes its self to overheat and short to ground. I have a motor just like yours in my shop right now. I can text pictures if you would like to see what happens when a deep cycle is used for cranking. I recommend fixing the battery drain and switching to an Interstate 24M-XHD before you wind up spending a lot of money in repairs.

Exactly the opposite. Deep-cycle batteries have thicker plates while cranking batteries have more plates but thinner ones. Plate surface area is what controls maximum output and charging current, so deep-cycle batteries charge a little slower with a little less current going in than cranking batteries.

The starter will pull exactly the same current from a battery no matter what kind of battery you have hooked up. Only the construction of the starter and the mechanical load of turning the outboard can change the current draw of the starter.

The heating of the charging system components in a stator based system is a function of the electrical usage between charges, not the battery technology. Modern boats with electronics and other equipment just use a lot of power and these charging systems aren't designed for the job. If you draw 5 amps for 2 hours from a battery, the load on the charging system to recharge the battery is going to be about the same and so is the heat. The charging system will be maxed out trying to recharge the battery whether it is a deep-cycle or a cranking battery.

Very few outboards with starter motors are rectifier only systems. Some very old ones still are, but most use combination rectifier/regulators to limit maximum charging voltage.

Outboard manufacturers misunderstand the issue and issue recommendations that don't really help. On a regulated system, Mercury still recommends against AGMs even though the AGM is substantially faster at charging which would reduce the overall power (and therefore heat) needed to be provided by the charging system because AGMs waste much less of the charging energy. An AGM is built like a starting battery with thin plates, but the starved electrolyte construction with the mats between the plates protects them from the deterioration deep-cycling would normally cause on the thin plates.

These new electronic devices, especially the Livescope, suck the juice out of a battery. I've thought about this all weekend. I think I'm going to go with a dual purpose cranking/trolling battery.

Just a thought but, are you actually charging your starting battery or are you simply relying on your motor's alternator?

If the answer is "yes" to the second part of the question, I suspect you are using more juice than you are replacing and I suggest purchasing/installing an onboard battery charger that will charge your trolling motor batteries as well as your main battery. If however you are charging your battery, it could be as simple as you having a bad battery that will not take a full charge.

I do have a on board charger for both trolling batteries and starting battery that is plugged in as soon as I get back home. I usually only crank my motor 3-4 times on a trip. I know adding another battery for the live well and electronics would be the best choice but I was trying to get around another battery and another charger if I could. I don't want to have expensive electrical repairs either.

Originally Posted by deltarat

I do have a on board charger for both trolling batteries and starting battery that is plugged in as soon as I get back home. I usually only crank my motor 3-4 times on a trip. I know adding another battery for the live well and electronics would be the best choice but I was trying to get around another battery and another charger if I could. I don't want to have expensive electrical repairs either.

I have a 50 four stroke Yamaha. I run 2 depthfinders, a 12 volt air pump and my livewell pump on a timer from the time I put it in the water until I take it out. Had a 27 on it. That one went bad after about 5 years. Replaced it with one of the Exide group 24 dual purpose batteries from academy. Haven’t had a problem going on 2 years. Good sign of a good battery is battery weight. That exide is as heavy or heavier than the 27 deep cycle it replaced. All that weight comes from the lead plates. Heavier plates means longer life.

An easy way to check if the charging system is working is to look at the tach. The tach works off of the rectifier and stator. If the tach is not working, check the back of the tach to see if it has a good 12v supply, with the key on and a good ground. If both are good and it still doesn't work, there is a problem somewhere in the charging system.