Marine battery selection
I'm going to start by saying that I am by no means an expert on marine batteries. That being said, I've done my homework and feel I can offer some educated advice on the subject. This post is going to concentrate on dual purpose marine deep cycle batteries for use as a trolling motor battery. Dual purpose marine batteries are very common nowadays. These batteries have sufficient reserve capacity to use as a trolling battery and sufficient cranking amps to use as a starter battery. In theory, a single battery could be used for both trolling and starting. I don't recommend this unless you have a way to manual (pull start) your engine.
So what should you be looking for in a trolling motor battery? The simple answer is Reserve Capacity. What the heck is reserve capacity you ask? I did too. Reserve capacity is simple; the length of time, in minutes, a battery can operate at the industry standard measuring stick of 25amp draw. So if a battery has a Reserve Capacity of 100, it can operate for 100 minutes at 25amps. A good rule of thumb for trolling motors is .75amps per lb of thrust for a 24V trolling motor and 1amp per lb of thrust for a 12V trolling motor. Don't get caught up in the math because it's real simple: the higher a battery's reserve capacity, the longer you can troll.
For some, like myself, it's not always that simple. You have to consider things like: How much room do I have in my battery compartment? Is weight a factor? Will I store my boat for long periods of time? What's my budget?
There are 3 types of batteries to choose from: Lead Acid, Absorbed Glass Mat (AGM), and Gel. We won't talk much about Gel because I don't think it's worth the time and effort for a battery that's all but been made obsolete by AGM's. That being said the debate is down to Lead Acid and AGM. Let's take a look at the pros and cons for both types.
LEAD ACID
PROS:
High Reserve Capacity
Low weight
Reserve capacity to weight ratio (High reserve capacity in lower weight)
Low cost
Readily available
CONS:
Typically 3-5 year battery life
Don't respond well to being stored for long periods - need a float charger or battery tender
Some require adding water
AGM
PROS:
5-10 year battery life
Maintenance free
Readily available
CONS:
High cost
Reserve capacity weight ratio (need a heavier battery to get the reserve capacity of a lead acid)
Needs a high amperage charger to achieve the advertised charge times
I can make a strong argument for either type, however based on the pros and cons I've listed you can ask a couple simple questions to make your decision easy:
1) #1 most important what is you budget? If you want AGM's with high reserve capacity be prepared to pay at least $200 per battery. A comparable Lead Acid battery runs about $100.
2) Will you take care of your batteries? By this I mean placing them on the charger as soon as you get back from the lake. Leave them on a float charger when stored. Add water as needed? (i.e. you are not prone to forget to do this). If you answered NO to any of these questions, you should probably opt for an AGM. AGM's are much more tolerant to "dummy" battery care.
3) Is size and/or weight an issue? A typical 29 series lead acid battery weighs in around 62lbs. A 31 series AGM (same footprint as the 29 series lead acid) can be 5-15lbs heavier.
Here is a list of some of the best AGM batteries out there. Included on the last line is the best lead acid battery on the market, and yes, it's from Walmart. No other lead acid even comes close to the reserve capacity of the Walmart Marine Maxx-29 so it's the only one I'll compare to the AGM's. The prices listed below are based on the cheapest I could find them on the internet. This list is certainly not all-inclusive.
An interesting factoid on Sears Marine Platinum AGM's: they are the exact same battery as the much more expensive Odyssey Trolling Thunder AGM. In addition, sears has a 5 year warranty and you will always be able to find a Sears to exchange your battery. Moral of that story is don't waste your money on an Odyssey battery just to get the name.
A common misconception on AGM batteries is that they last longer. This is due to some tricky marketing by the battery makers. The life of an AGM battery is longer than a lead acid battery not how long they last on the water. The reserve capacity is the way to compare how long they will last on the water. If an AGM has an RC of 200 and a lead acid has the the same RC they will last the same amount of time on the water. AGM's don't last longer on the water than lead acid batteries with comparable reserve capacity.
Understanding battery care: No battery will achieve it's maximum life without proper care. Batteries hate to be stored for any amount of time with less than a full charge. That's why it's essential to put your batteries on the charger immediately when you get home from the lake and leave them on the charger in float mode (or a battery tender). AGM's are much more tolerant than lead acids in this regard but even AGM battery life will be reduced if stored with less than a full charge.
Summary: In my humble opinion AGM batteries simply aren't worth the extra cash for the average fisherman. If you have a 3 stage charger, which most on-board chargers are, then you have a float stage on your charger. If you put your batteries on the charger as soon as you get back from the lake, leave them on the charger (if it has a float stage) until you go out next, and check the water on a regular basis, your lead acid batteries will have a long life. I think a lot of the AGM craze is two fold 1) it's the latest technology and some guys feel like they have to have all the latest and 2) due to tricky marketing they think they'll give them more trolling time.
I'll be going with the Walmart Everstart Maxx-29 this year. At $75 a pop, a 3-year no questions asked return policy, only 62lbs, and reserve capacity comparable to a $250 AGM, it's hard to argue otherwise.
So what should you be looking for in a trolling motor battery? The simple answer is Reserve Capacity. What the heck is reserve capacity you ask? I did too. Reserve capacity is simple; the length of time, in minutes, a battery can operate at the industry standard measuring stick of 25amp draw. So if a battery has a Reserve Capacity of 100, it can operate for 100 minutes at 25amps. A good rule of thumb for trolling motors is .75amps per lb of thrust for a 24V trolling motor and 1amp per lb of thrust for a 12V trolling motor. Don't get caught up in the math because it's real simple: the higher a battery's reserve capacity, the longer you can troll.
For some, like myself, it's not always that simple. You have to consider things like: How much room do I have in my battery compartment? Is weight a factor? Will I store my boat for long periods of time? What's my budget?
There are 3 types of batteries to choose from: Lead Acid, Absorbed Glass Mat (AGM), and Gel. We won't talk much about Gel because I don't think it's worth the time and effort for a battery that's all but been made obsolete by AGM's. That being said the debate is down to Lead Acid and AGM. Let's take a look at the pros and cons for both types.
LEAD ACID
PROS:
High Reserve Capacity
Low weight
Reserve capacity to weight ratio (High reserve capacity in lower weight)
Low cost
Readily available
CONS:
Typically 3-5 year battery life
Don't respond well to being stored for long periods - need a float charger or battery tender
Some require adding water
AGM
PROS:
5-10 year battery life
Maintenance free
Readily available
CONS:
High cost
Reserve capacity weight ratio (need a heavier battery to get the reserve capacity of a lead acid)
Needs a high amperage charger to achieve the advertised charge times
I can make a strong argument for either type, however based on the pros and cons I've listed you can ask a couple simple questions to make your decision easy:
1) #1 most important what is you budget? If you want AGM's with high reserve capacity be prepared to pay at least $200 per battery. A comparable Lead Acid battery runs about $100.
2) Will you take care of your batteries? By this I mean placing them on the charger as soon as you get back from the lake. Leave them on a float charger when stored. Add water as needed? (i.e. you are not prone to forget to do this). If you answered NO to any of these questions, you should probably opt for an AGM. AGM's are much more tolerant to "dummy" battery care.
3) Is size and/or weight an issue? A typical 29 series lead acid battery weighs in around 62lbs. A 31 series AGM (same footprint as the 29 series lead acid) can be 5-15lbs heavier.
Here is a list of some of the best AGM batteries out there. Included on the last line is the best lead acid battery on the market, and yes, it's from Walmart. No other lead acid even comes close to the reserve capacity of the Walmart Marine Maxx-29 so it's the only one I'll compare to the AGM's. The prices listed below are based on the cheapest I could find them on the internet. This list is certainly not all-inclusive.
| Battery | Series | Ah | RC | price | weight | ||||
| Trojan 24-AGM | 24 | 76 | 137 | $255.00 | 42 | ||||
| Optima D34M | 34 | 55 | 120 | $165.00 | 43.5 | ||||
| Odyssey Trolling Thunder 34M | 34 | 68 | 135 | $250.00 | 49 | ||||
| DieHard Marine Platinum PM-2 34M | 34 | 68 | 135 | $200.00 | 53 | ||||
| Optima D27M | 27 | 66 | 140 | $190.00 | 54 | ||||
| Optima D31M | 31 | 75 | 155 | $204.00 | 60 | ||||
| Trojan 27-AGM 12V | 27 | 89 | 158 | $264.00 | 64 | ||||
| Lifeline GPL-27T | 27 | 100 | 186 | $260.00 | 65 | ||||
| Lifeline GPL-31T | 31 | 105 | 195 | $280.00 | 69 | ||||
| Trojan 31-AGM 12V | 31 | 100 | 177 | $380.00 | 69 | ||||
| DieHard Marine Platinum PM-1 31M | 31 | 100 | 205 | $250.00 | 75 | ||||
| Odyssey TT 31M-PC2150ST | 31 | 92 | 205 | $323.00 | 78 | ||||
| Lifeline GPL-30HT | 31 | 150 | 315 | $400.00 | 96 | ||||
| Walmart Everstart MAXX-29 | 29 | 125 | 205 | $75.00 | 65 |
An interesting factoid on Sears Marine Platinum AGM's: they are the exact same battery as the much more expensive Odyssey Trolling Thunder AGM. In addition, sears has a 5 year warranty and you will always be able to find a Sears to exchange your battery. Moral of that story is don't waste your money on an Odyssey battery just to get the name.
A common misconception on AGM batteries is that they last longer. This is due to some tricky marketing by the battery makers. The life of an AGM battery is longer than a lead acid battery not how long they last on the water. The reserve capacity is the way to compare how long they will last on the water. If an AGM has an RC of 200 and a lead acid has the the same RC they will last the same amount of time on the water. AGM's don't last longer on the water than lead acid batteries with comparable reserve capacity.
Understanding battery care: No battery will achieve it's maximum life without proper care. Batteries hate to be stored for any amount of time with less than a full charge. That's why it's essential to put your batteries on the charger immediately when you get home from the lake and leave them on the charger in float mode (or a battery tender). AGM's are much more tolerant than lead acids in this regard but even AGM battery life will be reduced if stored with less than a full charge.
Summary: In my humble opinion AGM batteries simply aren't worth the extra cash for the average fisherman. If you have a 3 stage charger, which most on-board chargers are, then you have a float stage on your charger. If you put your batteries on the charger as soon as you get back from the lake, leave them on the charger (if it has a float stage) until you go out next, and check the water on a regular basis, your lead acid batteries will have a long life. I think a lot of the AGM craze is two fold 1) it's the latest technology and some guys feel like they have to have all the latest and 2) due to tricky marketing they think they'll give them more trolling time.
I'll be going with the Walmart Everstart Maxx-29 this year. At $75 a pop, a 3-year no questions asked return policy, only 62lbs, and reserve capacity comparable to a $250 AGM, it's hard to argue otherwise.
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