Keeping your deep cycle batteries healthy and happy...

Discussion in 'Boat Repair Help' started by dixiedrifter, Apr 26, 2006.

  1. dixiedrifter

    dixiedrifter New Member

    Messages:
    102
    State:
    Tennessee
    There is a lot out there to know about batteries and how to keep them healty and happy for a long time.

    Here are some random pointers:

    Slower discharging rates are more efficiant. That means you would be better off having two batteries hooked parallel for your electrical subsystem rather than having two separate batteries. Its easier on your batteries and gives you more power.

    True deep cycle batteries have solid lead plates in them. Most marine batteries are a hybrid starting/deep cycle type battery using a course lead sponge for plates. Batteries can have several types of electrolite configurations. There is the standard flooded, gelled, and absorbed glass mat or "AGM".

    In my opinion, gelled batteries should be avoided for boat use unless you are equipped to charge them properly, and since AGM batteries cost 2-3 times more than flooded, you can replace them once and still come out ahead. And, the only real diffrence between battery brands is the way the plates are constructed, better batteries will have better plates that are less subject to damage from physical shock and vibration.

    True industrial deep cycle batteries should not be discharged below 20% "depth of discharge" and most "commonly found in supercenter stores everywhere" marine batteries should not be discharged below 50% capacity for maximum life. A common marine type deep cycle battery that is subjected to depth of discharge cycles of 50% will last twice as long as a battery that is discharged to 20%. Occasional drops below 50% are generally not harmful to your batteries, but repeated deep discharges are.

    Remaining battery capacity can be measured by its voltage or specific gravity. Since its impossible to check the specific gravity of some cells due to sealed vents, usually the only option is to do a voltage check. Flooded cell batteries voltage should be checked several hours after charging and then after a few minutes under load from something like a small light bulb. The reason for this is it takes time for the electrolyte to equalize.

    A normal fully charged battery will have an approximate charge of about 12.7 volts which steadily drops as it is used:

    90%=12.50
    80%=12.42
    70%=12.32
    60%=12.20
    50%=12.06
    40%=11.90
    30%=11.75
    20%=11.58
    10%=11.31
    00%=10.50


    Deep cycle batteries are rated by Amp-hour Capacity and how much battery capacity you carry with you should be adjusted accordingly. An amp-hour is just that, one amp draw per hour. Batteries are usually rated on the 20 amp-hour standard, meaning the battery it completly discharged over a period of 20 hours down to 10.5 volts while the total amp hours are measured. The average trolling motor draw on max setting is about 1 amp per 1 pound of thrust. So if you use a trolling motor with a 40 pound thrust on max, you will use approx 40 amp-hours of battery capacity per hour of use. Since batteries are rated at max depth of discharge, and you only want to do 50% discharge, you can cut their rated capacities in half right off the bat when estimating your needs.

    Batteries should probably be subjected to a load test periodically to determine their remaining amp-hour capacity, say at the beginning of each season. This will give you an idea of how much life is left in them and how long you can operate on the water.

    The #1 cause of premature battery failure is due to failing to recharge a discharge cell within 12-24 hours. The sooner you can hook a discharged battery to a charger the better. Letting a cell self discharge and failing to recharge for several months is even more deadly. Self discharge losses can be anywhere from 1-15% per month depending on type of battery. Contrary to belief, storing a battery on a concrete floor is OK. Used to be in old times the cases were made of wood and asphalt (which is not exactly the ideal container for acid) the electrolyte would slowly leak onto the floor causing a short.

    Overcharging is another big killer of batteries. Gel type batteries MUST be charged a lower amperage than regular flooded batteries. Otherwise voids may form in the gel which won't heal causing a loss in battery capacity. Using a regular car battery charger can and will damage them. AGM's can take much more abuse than either a flooded or gelled cell and have none of the disadvantages of gel cells.

    The proper amp charging rate is designated by the manufacturer and should not be exceeded regardless of battery type. Battery charging is divided into three stages, bulk, absorbtion, and float.

    During the bulk stage, a charge is given to the battery at the maximum safe rate that can be accepted until the voltage gets to around 80-90% capacity. Voltage on the charger can be anywhere up to 15 volts, but the amps needs to be a set limit. Because of Ohm's law, voltage and amperage are directly related and need to be taken into consideration for the most rapid safe charge.

    Once the absorbtion stage commences, the voltage of the charger remains the same, but the amount of amps decreases due to internal resistance in the cells. This is where you need more volts to fully charge the battery in the least amount of time, again to Ohm's law. A good way to think of it is that 20 amp charger will only be pushing 5 amps when the battery is nearly fully charged.

    The last stage is where you "float" the battery. The charging voltage is usually around 12.8 volts. Float chargers use what is called "pulse width modulation" which senses tiny drops in voltage and sends short charging cycles to the battery which range from several microseconds to seconds.

    Keep in mind that most low end chargers are bulk charge only and have little or no voltage regulation which are not very good for your batteries as they can overcharge them.

    If your battery has lost a lot of its original capacity, you can equalize them. Equalization is a controlled overchaging of the battery to remove sulphation. If your charger has this feature, you put it into that mode once the battery has been fully charged and check the specific gravity of the cells once per hour. When the specific gravity stops changing, the battery has equalized and you get some of the amp-hour capacity back.
     
  2. LarryW

    LarryW New Member

    Messages:
    523
    State:
    Abbeville Louisiana
    Very good informative post with a lot of good information. Thank you for the information.
     

  3. dixiedrifter

    dixiedrifter New Member

    Messages:
    102
    State:
    Tennessee
    Believe it or not, and if I'm thinking correctly, Walmart's Everstart brand is made by Johnson Controls, the same company that makes the Optima batteries.

    http://www.jci.com/bg/products_brands.htm

    If you check out their site, it also explains why the Optima batteries are so much better and cost more, they are AGM instead of flooded cell.
     
  4. FishMan

    FishMan New Member

    Messages:
    2,293
    State:
    Tennessee
    really good post
     
  5. Cattledogz

    Cattledogz New Member

    Messages:
    1,374
    State:
    NC
    Great, very informative post! Thanks for sharing the info.
     
  6. Arkie55

    Arkie55 New Member

    Messages:
    669
    State:
    Mississippi
    Now that is a great post. We all need some knowledge about our power systems on our boats. I learned more about my battries from you post that I thought I would ever know. Thanks.
     
  7. dixiedrifter

    dixiedrifter New Member

    Messages:
    102
    State:
    Tennessee
    Here is some more info on the Optima batteries quoted from their website... take note that the 34M battery is NOT rated for deep cycle use!

    Blue Top Type: D34M / D31M
    These batteries are dual purpose. They are designed for engine starting and deep cycling applications and for use in boats with large accessory loads.

    Recommended charging information:

    Alternator:
    13.65 to 15.0 volts, no amperage limit.

    Battery charger:
    13.8 to 15.0 volts, 10 amps maximum, 6-12 hours approximate.

    Cyclic Applications:
    14.7 volts, no current limit as long as battery temperature remains below 125°F (51.7°C). When current falls below 1 amp, finish with 2 amp constant current for 1 hour for D34M and 3 amp constant current for 1 hour for D31M.

    Rapid Recharge:
    Maximum voltage 15.6 volts (regulated).
    Maximum current: No limit as long as temperature <125°F (51.7°C).
    Maximum recharge time: Charge until current drops below 1 amp.

    Float charge:
    13.2 to 13.8 volts, 1 amp maximum current, time indefinite (at lower voltage).

    All limits must be strictly adhered to.
     
  8. Kutter

    Kutter New Member

    Messages:
    5,379
    State:
    Arnold, MO
    I am a bit confused on what you are saying here. AGM are better, even if they cost more? Or because they cost more, they are not better than flodded batteries?
     
  9. dixiedrifter

    dixiedrifter New Member

    Messages:
    102
    State:
    Tennessee
    I was referring to flooded batteries being better bang for the buck.

    Obviously an AGM battery is technologically superior in many respects to a flooded cell.

    But are they really worth more than double the price of a regular flooded cell?
     
  10. brad kilpatrick

    brad kilpatrick New Member

    Messages:
    2,666
    State:
    Kansas City
    Dixie,
    I recently got a optima blue top 31m battery. i was planning on using it for running My trolling motor. Is it suited well to this task or would i be better off using it to start My 90hp merc?
     
  11. dixiedrifter

    dixiedrifter New Member

    Messages:
    102
    State:
    Tennessee
  12. brad kilpatrick

    brad kilpatrick New Member

    Messages:
    2,666
    State:
    Kansas City
    I think I misstated in My post but i got the info I needed all the same. The 34M is a starting battery only, but the D31M that I have is dual purpose for use starting or deep cycle use (like a trolling motor) according to the Optima website.

    I suppose the D befroe the number stands for dual purpose

    Thanks Jared, Your Info Was very good and helpful!!!!
     
  13. sgt_rob

    sgt_rob Member

    Messages:
    961
    State:
    Bossier City, LA
    Don't forget to check your water. I added about 3 pints of distilled water to mine this morning.