To deep cycle or not to deep cycle, that is the question.

[Musselwhite]

Is a deep cycle marine battery the way to go for trolling motors? Or, can I pick up an extra 12v car battery? Not starting an engine or running any other electronics. What do you guys use for your trolling motors?

Thanks.

Musselwhite

[knot trying]

A deep cycle battery was designed for the type of usage it would get running a trolling motor. (complete discharge/recharge).

A car battery is not designed with that type of cycle in mind and will not last.

[Jakal03]

I spoke in depth with a few people and did a lot of research when I bought my trolling motor regarding the differences between a Starting, Deep Cycle, and AGM battery. He told me that if I was going to be on a bass boat and subjecting the battery to lots of bumps and bangs, the AGM was the way to go. Otherwise a deep cycle. A deep cycle battery is designed to be discharged repeatedly by 80% or more and recharged again. Doing this with a starting battery will kill its life a lot quicker b/c of the way the lead plates are designed. Here is a good write up on each battery type that I found when doing my research:

* Starting (sometimes called SLI, for starting, lighting, ignition) batteries are commonly used to start and run engines. Engine starters need a very large starting current for a very short time. Starting batteries have a large number of thin plates for maximum surface area. The plates are composed of a Lead "sponge", similar in appearance to a very fine foam sponge. This gives a very large surface area, but if deep cycled, this sponge will quickly be consumed and fall to the bottom of the cells. Automotive batteries will generally fail after 30-150 deep cycles if deep cycled, while they may last for thousands of cycles in normal starting use (2-5% discharge).

* Deep cycle batteries are designed to be discharged down as much as 80% time after time, and have much thicker plates. The major difference between a true deep cycle battery and others is that the plates are SOLID Lead plates - not sponge. This gives less surface area, thus less "instant" power like starting batteries need.

Unfortunately, it is often impossible to tell what you are really buying in some of the discount stores or places that specialize in automotive batteries. The golf car battery is quite popular for small systems and RV's. The problem is that "golf car" refers to a size of battery, not the type or construction - so the quality and construction of a golf car battery can vary considerably - ranging from the cheap off brand with thin plates up the true deep cycle brands. In general, you get what you pay for.

* Marine batteries are usually a "hybrid", and fall between the starting and deep-cycle batteries, though a few are true deep cycle. In the hybrid, the plates may be composed of Lead sponge, but it is coarser and heavier than that used in starting batteries. It is often hard to tell what you are getting in a "marine" battery, but most are a hybrid. Starting batteries are usually rated at "CCA", or cold cranking amps, or "MCA", Marine cranking amps - the same as "CA". Any battery with the capacity shown in CA or MCA may not be a true deep-cycle battery. It is sometimes hard to tell, as the term deep cycle is often overused. CA and MCA ratings are at 32 degrees F, while CCA is at zero degree F. Unfortunately, the only positive way to tell with some batteries is to buy one and cut it open - not much of an option.


*AGM, or Absorbed Glass Mat Batteries- A newer type of sealed battery uses "Absorbed Glass Mats", or AGM between the plates. This is a very fine fiber Boron-Silicate glass mat. These type of batteries have all the advantages of gelled, but can take much more abuse. These are also called "starved electrolyte", as the mat is about 95% saturated rather than fully soaked. That also means that they will not leak acid even if broken.

AGM batteries have several advantages over both gelled and flooded, at about the same cost as gelled:

Since all the electrolyte (acid) is contained in the glass mats, they cannot spill, even if broken. This also means that since they are non-hazardous, the shipping costs are lower. In addition, since there is no liquid to freeze and expand, they are practically immune from freezing damage.

Nearly all AGM batteries are "recombinant" - what that means is that the Oxygen and Hydrogen recombine INSIDE the battery. These use gas phase transfer of oxygen to the negative plates to recombine them back into water while charging and prevent the loss of water through electrolysis. The recombining is typically 99+% efficient, so almost no water is lost.

The charging voltages are the same as for any standard battery - no need for any special adjustments or problems with incompatible chargers or charge controls. And, since the internal resistance is extremely low, there is almost no heating of the battery even under heavy charge and discharge currents. Most AGM batteries have no charge or discharge current limits.

AGM's have a very low self-discharge - from 1% to 3% per month is usual. This means that they can sit in storage for much longer periods without charging than standard batteries.

AGM's do not have any liquid to spill, and even under severe overcharge conditions hydrogen emission is far below the 4% max specified for aircraft and enclosed spaces. The plates in AGM's are tightly packed and rigidly mounted, and will withstand shock and vibration better than any standard battery.

Even with all the advantages listed above, there is still a place for the standard flooded deep cycle battery. AGM's will cost 2 to 3 times as much as flooded batteries of the same capacity. In many installations, where the batteries are set in an area where you don't have to worry about fumes or leakage, a standard or industrial deep cycle is a better economic choice. AGM batteries main advantages are no maintenance, completely sealed against fumes, Hydrogen, or leakage, non-spilling even if they are broken, and can survive most freezes. Not everyone needs these features.

[Musselwhite]

Thanks for the info, guys. The AGM is new to me. I think I will go with the deep cycle this go'round. In a few years I'll realize I should have forked out extra money on the AGM.


Musselwhite

[Jakal03]

I originally set out to buy an AGM..........until I found out that it was gonna cost nearly twice as much as my motor :yikes:. I settled with a deep cycle and it does just fine for what I need it to do.

[FairWeatherFisherman]

IMHO the lower risk of venting hydrogen and the potential explosion outweighs the cost. No way I would ever buy another non-AGM battery for a boating application.

[harleysilo]

I use your standard run of the mill Deep Cycle Marine battery from autozone or autoparts pluse etc.

Weights a ton, I put it in the front of my canoe to offset me. I bought some long wire at Home depot and run the power back to the rear of my canoe where the motor is.

I've never run the battery down significantly using the trolling motor. I imagine I could run the trolling motor wide open for hours. I guess I could calculate that but why?