This is from another site. Maybe it will help a little


Hey if figured this is my q to chime in. thanks for the props h20, it was a pleasure meeting you at the novi show!!
Gitzit, the first thing i would ask you is how many times a year do you fish? also do you maintain the batteries in the winter?
I recommend for the average fisherman who fishes 10-15 times a year, a standard wet cell deep cycle battery. The reason is this. I find the majority of customers forget to maintain the batteries in the offseason and the batteries then become sulpahated. The same will happen with a AGM battery. Why kill an expensive battery like the AGM. If you do maintain the regular deep cycle batteries in the off season, then you should expect 4-5 years or more! I Recommend brands like Exide or Deka or even the everstart. if you ask 10 guys what they recommend youl usually get at least 8 different answers.

If you fish alot more than the average joe, but not like some of the diehard tournament guys that fish say 100 days or more a year, and you are strict on maintaining your batteries, AGM's ar a great way to go. The downside to this is they are a little pricey up front, but as h20 says you make it up in the long run.


Note: When you compare Statistics like AH (Amp Hour) Rating it may seem a litte decieving.
Example: Optima Bluetop D34M and Exides ORB34DC36 are rated at around 55 Amp Hours.
Compare that to a regular wet cell D/C Battery like the a Group size 24 D/C which is usualy around 75 Ah, or compare it to a group size 27 D/C which is usually around 90-100 AH, you would think it would make sense to use the 27's or even 24's for longer run time. However, I have alot of local bass pros that use 3 Optima's in place of 3 group 24's or even 3 group 27's, and they getting better longevity out of their optimas\orbitals than with the regular wet cell batteries. Why is this? I think it comes down to the construction and design of the AGM's. For one, AGM's are made with 99.9% pure lead, while regular batteries are usually made with less Pure lead and even recycled lead. which in turn, has a lot of internal resistance(OHMS).because of the pure lead, AGM"S have a very low Internal Resistance (OHMS) raitng than regular batteries.
Internal Resistance is also what causes a battery to self disharge when sitting. The lower the rating the, the longer the shelf life! Also batteries will except more from the charger, faster, when a battery has lower internal resistance. Thats why a discharged AGM can usuall get to 90% in 1 Hour on a 50 amp Charger!.
another thing that a lower internal resistance rating equates to is a higher voltage when under load.
For instance a car's starter will draw a battery down to about 10.2 volts when the key is engaged. but with agm that voltage is usually around 11V. The higher the voltage, the faster the starter will spin. Make sense? I hope so.

I have bass pros that use optimas, orbitals and regular Deep cycle batteries as well. One Bass guy i sponsor uses Exide NG31's, regular wet cell D/C in the Group 31 size. he gets more out of these than an smaller Optima\Orbital battery. Others are using the Exide orb34DC36 or the BLUETOP D34M. there are alot of different situations which call for a certain battery.

Now a serious bass pro that fishes 100+ days a year will usually only get 2 years out of either type of battery. Deep cycle batteries only have so many cycles usually around 250-300.

2 Optimas BluetopD34M are going to run you about $350-$390 + Core
2 Orbitals ORB34DC36 for about $280 + core
2 regular 27DC around $69-$79 + core

I Recommend the Exide Orbital Marine # ORB34DC-36. It is a Spiral cell Orbital battery, just like the Optima, except it is roughly 30% cheaper and has a longer warranty period(18 Months free replacement, 36 months prorated, as opposed to Optima's which is 1 year free replacement, 24 Months pro-rated). It will give you the same results as most standard 27 D/C Batteries will.


Hope i have helped

Regards,
the "BatteryMan"
Rob Dumas