Batteries - Cranking vs. Deep Cycle

drjohn71a

I know there are a lot of battery experts here on the site who know all about the latest and greatest, the sealed, the gel, etc. batteries. However, I had the opportunity to talk to the head mechanic at one of the larger marinas on Grand Lake, OK about batteries.

I was showing him my "Quick-Fill" hoses which I had run to top off the water levels in my hard to reach batteries since charging them seemed to run all the water out - just like my motorhome house batteries.

The old guy (in his early 80s') said that they only stock and advise installing ONLY cranking type batteries. He said that the engine charging systems and the shoreline charging systems on boats rapidly boils the water out of the Deep Cycle type of batteries, but does not effect the cranking type of batteries.

He advised installing only cranking type batteries of 850 cranking amps or more. He said they follow this rule even on the 80-100 foot boats in that area since the batteries are often in out of the way places and often ignored as far as water goes.

Soooo, what do you resident experts think of this? It kind of does make sense considering how rarely we have to top off the water in our truck, tractor and boat starting batteries.

John

mikeporterinmd · Posted: Mon Aug 20, 2007 12:38 pm Post subject:

A charger with a temp sensor shouldn't boil the water out. But, since
I only have cranking batteries at the moment because that is what
the boat came with, I can't prove that.

Mike

BrentB · Posted: Mon Aug 20, 2007 1:55 pm Post subject:

I agree. I plan to purchase a battery charger with temp sensor, document the voltage before taking off or some regular occurence and avoid discharging each battery below ~55 -60%. I buy batteries from Wal-Mart and appreciate their free old battery disposal. I use marine deep cycle batteies.
m2cw

drjohn71a · Posted: Mon Aug 20, 2007 2:45 pm Post subject:

How would an alternator know you had installed a temp. sensing shore charger?

John

BrentB · Posted: Mon Aug 20, 2007 3:39 pm Post subject:

Dr John

The alternator would not know unless you replace it with one that has it builtin, if it is exists or inline temp sensor. The unit I was plannning to purchase is a separate system and was discussed by Dr Bob (Thatway) is an earlier post. I believe it was made by Xantrex
www.xantrex.com

BrentB · Posted: Mon Aug 20, 2007 3:41 pm Post subject:

Description

Xantrex' Battery Temperature Sensor is designed for use with DR and UX Inverters and C Series Charge Controllers. The BTS mounts on a terminal post of a battery in a bank or on the side of a battery and measures its temperature. It sends precise information to the charger or charge controller, which automatically adjusts voltage to ensure full battery charge depending on the ambient temperature of your battery installation. The BTS is standard on SW and PS Inverters.
http://www.xantrex.com/web/id/105/p/1/pt/5/product.asp

drjohn71a · Posted: Mon Aug 20, 2007 4:03 pm Post subject:

Thanks for the info.

I guess what I am saying is that the charging control systems commonly installed on boats boils the water out of the deep cycle batteries and that cranking batteries do not have this problem. That is according to the old mechanic.

So, my question is not so much,"How much money can we throw at that problem?", as much as it is,"Does it make sense to install cranking batteries only if you are not wanting to rewire your boat's charging system?"

I just paid a fortune for a new boat and I am not wanting to rewire it already!

John

BrentB · Posted: Mon Aug 20, 2007 4:39 pm Post subject:

drjohn71a · Posted: Mon Aug 20, 2007 5:04 pm Post subject:

Brent,

What I am saying has nothing to do with 'sealed' batteries. The fact is that cranking batteries are more compatible with the supplied charging systems on most boats, cars, trucks, and RVs and, as such, do not suffer the rapid water loss that deep cycle batteries do.

John

BrentB · Posted: Mon Aug 20, 2007 5:23 pm Post subject:

ok Dr John I understand.

Either battery type does the same job then needs to be recharged after the egnine is started then waits until it is needed again.
I have a deep cycle just to start motor and it gets recharged after each use and does not suffer rapid lost. Its problem is not enough use and loses its charge over time. Poor thing, I just go a new one. Batteries are like hard drives. Time not usage causes failures.

oldgrowth · Posted: Mon Aug 20, 2007 8:02 pm Post subject:

drjohn - I am not a battery expert so I don’t know the answer to your question, but it sounds like it could be true but that doesn’t mean that it is.

I will monitor my battery a little closer to see if it is happening.

I have a starting battery and a group 28 house battery. I do have a BlueSea automatic battery combiner that will disconnect the house battery if the charging voltage gets too high, so this might protect it from boiling the water.

I would like to hear from Joe and Dr Bob or anyone else that knows the answer.
________
Dave

Sea Wolf · Posted: Mon Aug 20, 2007 8:43 pm Post subject:

Dave-

I really don't know the answer, either!

I'd really have to do some serious research to give you an intelligent answer.

What I do, is what Brent does, buy deep cycle batteries from Wal-Mart and keep them charged diligently.

I do suspect (to borrow one of Dr. Bob's lines) that the proposition that cranking batteries are less subject to overcharging and water loss to be a gross oversimplification with perhaps some truth to it, although there's be many counter arguments. Batteries are a very complex subject, involving a whole range of chemical and electrical issues!

It certainly justifies the "old man" not having to stock a wide variety of battery types and sizes! Wink

Joe.

gljjr · Posted: Mon Aug 20, 2007 8:54 pm Post subject:

This seems like hawgwash to me. As a former mechanic I've replaced LOTS of batteries and I never saw the boiling of batteries on RV's that you are talking about EXCEPT when there is a problem with the charging system over charging the batteries.

I run inexpensive Costco Marine/Deep cycle batteries in my sled and have never had a problem with them boiling. Getting discharged from sitting is my usual problem. I'll be running similar batteries in the C-Dory when I get her running. Maybe in a few years when the prices come down a little more I'll go the AGM route. I've got one for my camper and it works great! Far more convenient than the standard Deep Cycle, and they stay charged over longer periods.

Sneaks · Posted: Mon Aug 20, 2007 8:59 pm Post subject:

Well I have to disagree with your 80 year old mechanic. All lead/acid batteries will boil away water if the *maintenance* voltage is too high, be they deep cycle or cranking. Boaters (and RV'ers) have a tendency to overcharge, and the usual suspect is the charger itself. How many regular motor vehicle owners keep chargers plugged in and operating 7/24 even if they leave the car parked for a few weeks? Some RV'ers only unplug while moving from campground to campground and some boaters keep their chargers plugged in whenever they're not actually boating.

It takes a quality charger to safely charge and maintain lead acid batteries. At least without constant temperature and voltage monitoring, it does. Consider this:

Most cranking batteries are charged between 13.56 to 14.16 volts. At 14.22 volts and above, most start gassing and that means boiling away water. So you will notice the difference between a good charge and a damaging charge is only .08 volts! The recommended "float" or maintenance charge/voltage for lead acid batteries isn just 13.5 volts.

As a small example, our RV has two big 6 volt DC golf cart house batteries and they were constantly requiring water even though the on board charger/maintenance unit was highly rated. The problem? We were on shore power most of the time and the charger was set up for RV units that dry camped a lot. Quick charging was the priority. For us, it was just a matter of changing the charger's "priority". With 13.5 volts provided by our solar cell powered charger, I very rarely hve to water those puppies. It doesn't take much to maintain, so I would personally recommend just buying a maintenance charger, set it to 13.5 volts and leave the big gun charger for the marinas when you overnight after using those batteries as a power source all day.

Don

thataway · Posted: Mon Aug 20, 2007 8:59 pm Post subject:

If you are having a problem--a solution is "Hyrdo Caps" These are battery caps which have a platinum catalyst which allows the water and oxygen to be recombined and drip back into the battery.

I have never heard that starting batteries have less gassing and water loss than deep cycle batteries. Starting batteries have thinner plates (.04") vs deep cycle (.08 to .11) or Surrette (.15) or traction batteries (.25"). Generally deep cycle batteries use a lead cadmium mixture in the plates, which has less self discharge, and gassing--Some of the larger batteries us Lead antimony batteries, which will have more gassing and water, but these are the traction type of batteries--not the ones we use in our boats.

We have used gold cart batteries for over 25 years in our cruising boats. We would have 1200 amp hours of deep cycle batteries, and charge them about 2 hours a day, with a 130 amp charger and a 150 plus an 80 amp alternator. These would run the sailboat for the next 24 hours, including auto pilot, nav lights and instruments, etc.

Starting batteries are designed for high load output over short peroids, and discharge of 25 to 30% Deep cycle batteries are designed for 50% discharge over a long peroid of time with a modest current draw. It would be a step backward to use starting batteries for house in a boat which had significant demand when the engine is off.

Some of the external alternators do have temp compensator circuits. Ample power has made temp compensated external regulators--which could be hooked up to an outboard regulator. My Suzuki's have 14.4 volts which may not be as well regulated as ideal, but we have not have excessive gassing or water boil off.