Battery Care and Chargers

Article by Campbell Boat Owner Ron Fasola, owner of "Strange Brew"

Every boater makes a decision, whether he knows it or not, about how he intends to deal with his boat's batteries.  His decision can range from totally ignoring them to going arguably overboard on maintenance.  Ignoring batteries results in not only needing to buy batteries much too often, but also interferes with the boating experience, (by having to fix things while family and guests wait), even to the point of affecting safety, (getting stranded on the lake).  Ignorers sometimes end up buying new batteries almost each year in the worst cases, while maintenance freaks can get up to about 4 or maybe 5 years on a set.

For all but the ignorers, some type of charging method while the boat is in storage or idle is required.  At the bottom end are inexpensive trickle chargers that produce a small charging current either continually or for a set number of hours per day via some type of timer.  These types of chargers have no way to monitor the condition of the batteries, hence they do not vary the charging current in accordance with the batteries' needs, and they therefore go through battery water (acid) at a fairly high rate.  At the high end of the scale are the marine battery chargers, which range in price commensurate with features, but are generally more expensive.  They are designed to be permanently installed on a boat and plugged in to an AC outlet in a slip or when the boat is on its trailer.  Some marine chargers can charge any type of battery, can monitor the individual batteries and provide them a charging current based upon its specific needs, and do a host of other niceties.  Almost all marine chargers automatically shut off the charging current when the battery is fully charged, and automatically begin charging again when the battery begins to run low on charge. It will take a couple of seasons for a quality marine charger to pay for itself in new battery costs, (after which you're saving money forever), but in addition, when properly installed, battery related problems should be close to zero from the time of installation.

One high end marine charger is a TrueCharge 20+, (recently replaced by an improved model, the TrueCharge2), made by Xantrex.  The improved model weighs 4.8 lbs, and is roughly 3"x7"x10" in size, and costs about $210.  A detailed installation of a TrueCharge 20+ charger on a 24' Cuddy Campbell that lives on a trailer in Lake Havasu, Arizona, follows.  This particular charger was chosen for these reasons:

         - The boat has 2 batteries, and this unit can handle up to 3 batteries independently.

         - The charger is capable of producing up to 20 amps if it needs to, so it's not a lightweight.

         - The charger has an inexpensive temperature sensor option that suits Havasu's 30 to 130 degree ambient temperature swings.

         - The charger has settings for 2 or 3 stage charging, plus an equalization feature that can help prevent battery sulfation.
            The TrueCharge 20+ charger has a bulk, absorption, and float charge.

         - The charger can charge flooded, AGM, gel, or lead calcium batteries.

         - The charger has a host of safety protection features.

A call to Xantrex's tech department to discuss this application revealed:

         This would be a good charger for this AZ application, as long as the charger has adequate ventilation.

         The AC input wires for the 20+ are about 6 inches of exposed wires.  These wires are to be wired to either a panel, an extension cord for dockside plug in, or to an onboard receptacle that would accept a dockside extension cord.

Because the application's ambient temp goes from low 30's to 130, their battery temp sensor option is a good idea.  It will vary the charge amount according to the temp of the battery.  It will override the manual temp setting on the unit.  The sensor plugs into the charger and its other end is connected to a battery terminal.

It is preferable to wire the DC output of the charger directly to the batteries, (charger wire should be on top of the big battery cables), because wiring to the back of the battery switch would mean going through the positive cables, and the charger will see a higher load, and therefore it will charge at a higher rate and for a longer time than is necessary.  Furthermore, if the battery cables are or become marginal, they would then interfere with proper charging.  Direct wiring from the charger to the batteries removes the cables from the equation.

To check battery cable size, they use a figure of 0.2V maximum drop through the cables as their rule of thumb.  Drops over that indicate the need for larger or newer cables.  This is easy to check; compare voltage readings at the back of the battery switch with readings at the batteries.  Typically, charged batteries should read 13.5 V.

Reading the manual that came with the charger, it was learned that:

1.      The charger will be OK for Group 24 batteries.

2.      At over 110 degrees ambient, the charger will cycle on/off at high charge rates.

3.      Every 15 minutes, the charger will stop for 5-30 seconds to check the state of the batteries.

4.      Every 2-4 months, one should manually trigger the charger to equalize while being observed. During this equalization cycle, one should monitor the Specific Gravity of the batteries and stop the cycle when/if the SG is 1.265 in all cells and is constant for three hours.  Repeat the equalization cycle if SG doesn't come up and stay.  The process needs to be monitored closely, because high current is being delivered to the batteries, which means much gassing will occur.  So distilled water might need to be added every few hours, and any acid over fills need to be wiped up immediately.  Good ventilation is a must during equalization.

The newer TrueCharge2 can be mounted in any position.  This charger was mounted under the shotgun seat in this Campbell.  The seat is left off for ventilation when the boat is stored on its trailer and under its cover.  8 gauge wire was used for the DC output, and 12 ga for the AC input, (a new orange extension cord plug end was cut off and soldered onto the charger's leads).  Positive output wires were 6 and 8 ft. long respectively, Negative output was 6 ft.  Battery cables were 2/0 sized, so there was no voltage drop through them compared to the voltage at the batteries.  The equalization mode was activated for only just about hour, the voltage was about 14 plus during this time.  Much gassing was noted.  It was confirmed that the charger begins its charge cycle every time it is connected, so watch for this!  The charger did get warm to the touch during the first big charge.

All that has been needed since the installation of the marine charger is periodic checking and filling of the water levels, (one STILL needs to check water levels, but not nearly as often).


Equilization: (From Trojan Battery's website, regarding their deep cycle batteries)

         Should be done on a regular basis.

         Should be done when the Specific Gravity is below 1.277 plus or minus 0.007 @ 80 degrees F.

         Should be done if any cell is 30 points below the SG of the other cells.

         Should be done when one battery is more than 0.3 volts different from the other battery.

         In general, should be done about once every 10 cycles for deep cycle batteries.

Batteries will discharge about 4% per week at 80 degrees F, if left alone and are not on a charger.

Negative posts are 5/16 coarse threads, Positive posts are 3/8 coarse threads.  Use grease on the terminals after the cables and wires are attached to the terminals.

It pays to keep batteries clean.  Grimy battery tops can provide a path for current to flow between the terminals, thus drawing down the charge.

It used to be thought that storing batteries on cement floors would discharge or harm batteries.  That was indeed the case with batteries "back then", but now that virtually all batteries have hard polypropylene cases, there is no problem with storing them on cement floors.

To check if something in the wiring system is still drawing current when everything is supposed to be off, remove the negative cable and gently touch or rub it against the negative battery terminal in low light or in the dark.  If you see a tiny blue light, (spark), then something is "on" because trace current is flowing.  Use common sense about doing this test in the presence of gasoline or battery acid fumes.

Do not leave batteries on charge with the battery caps off or slightly off for venting purposes.  If a battery requires a high current to charge, battery acid will boil out (gassing) and shoot over everything close to it and make a royal mess.  The caps are designed to vent without losing acid.

Do not fill batteries to the bottom of the individual fill tubes; that's too high and spill-over will occur upon charging.  The plates must be covered at all times with acid or water, and the ideal fill level is just below the fill tubes.  When the water reaches the fill tubes, the surface tension of the water changes the look of the water when viewed from above and it changes from glassy to somewhat curved.  That curved look indicates the level is too high.

Once a battery that has some use or years on it has its acid level reduced to where its plates are exposed, the odds are that it will be impossible to bring it back to full power.  If the battery is new when its plates get exposed, or the plates are exposed for just a short time, it may be possible to bring it back to full life, but exposed plates usually mean battery death. 

Trickle chargers, now matter how low the trickle current, will burn off the acid level in batteries left on charge for months at a time much more dramatically than marine chargers, which shut off the charging current once the battery is fully charged.  It's possible to use trickle chargers if you constantly add battery water, (every 3 weeks or so), but it's not a convenient way to deal with batteries.

Stereo units, VHF radios, and many other electronics benefit from having their ground wires connected directly to a battery negative terminal to avoid "floating grounds" and their associated electrical noise problems.  But it's poor practice to have umpteen wires connected to a battery terminal.  Instead, use a multi connection buss, (available at West Marine, they're cheap).  Connect a 10 gauge multistrand black wire to a negative battery cable using an appropriate eye connecter, (don't use a spade connecter on anything on a boat), and connect the other end of the 10 ga wire to the 5 to 10 connection buss.  Then connect all your devices needing direct grounds to the buss using eye connecters.

Be careful how you use that big red battery switch.  Say you thought ahead and switched to battery 1 before you beached and turned on the stereo.  When the stereo dies, you've still got battery 2 to start the boat motor. So far you're OK, but on the way back to home, you switch to "both" thinking that both batteries will benefit from getting charged on the ride home.  Not good.  The problem is that most big red battery switches are not isolaters.  When switched to "both", the drained battery will begin drawing current from the good battery real quick, even as the alternator on the running engine tries to charge both batteries.  You could easily end up with two weak batteries.  So if one battery is discharged, fire up on the good one, then switch to the dead one once running so all the charging current from the alternator goes into the dead battery and the good battery does not get drained.

The typical types of batteries are starting batteries and deep cycle batteries.  Starting batteries provide more amps to start motors, but can't take full discharges very well.  They are constructed with more plates, (for higher amps), but these thin plates are more fragile than the plates in deep cycle batteries.  Deep cycle batteries are made with fewer but thicker plates.  They can sustain multiple discharges and are more robust, but they don't provide as many amps, even at full charge, as starting batteries.  If you typically run down batteries using stereo's or DC blenders, then a possible compromise is to use one battery of each type on your boat; a group 24 starter battery and a group 24 deep cycle battery.  Stay with the same group type, don't use a group 24 with a group 27 battery.  Obviously, switch to the deep cycle battery for beach activities.  Another option now available is to buy what are called "dual purpose" batteries; the next time you have to buy batteries.  They are a cross between a starter and a deep cycle battery, and their prices are also in the middle of the other two types.

Updated August 16, 2010

Since the above was written, more information on batteries has come to light both from personal experience and published articles.  Almost all the above information was intended for flooded cell type batteries, which is the most common type of marine battery in use today.  Although there are some flooded cell sealed batteries on the market, flooded cell marine batteries usually have removable caps and require routine and periodical distilled water addition.

However, there are other types of batteries that were not discussed above, like Gell cell and AGM (Absorbed Glass Mat) batteries, that although more expensive, are becoming more popular for good reasons.


The TrueCharger 20 marine charger made by Xantrex that I installed on my 24 ft. Campbell in 2001, does not have a method to detect and compensate for a battery cell which fails while the boat is in storage and on "charge".  When a cell failed in one battery in my boat, the battery appeared to the charger to require more charging amps because the battery naturally measured low on output.  So the charger eventually fed its max current of 20 amps continually to the battery with a bad cell, which resulted in a very hot battery and so much gassing that battery acid was sprinkled all over everything near the battery.  Fortunately, the situation was noticed before anything catastrophic happened, but there was quite a mess to clean up and some permanent etching of nearby parts was done.  I believe later and current Xantrex chargers are designed to prevent this situation.

After the flooded battery failure above, (the batteries did last 5 years, however, in a Havasu boat), the decision was made to switch to AGM batteries for these reasons:

1.      AGM batteries have sealed cells; so there is zero possibility that the above situation can ever occur again, (even if the case cracks).
2.      Using sealed batteries eliminates mandatory monthly battery checking and/or distilled water addition, which greatly simplifies boat storage maintenance.  There is no fear about leaving the boat unattended for time periods over a month during the hottest part of the summer.
3.      The "old" Xantrex charger I have DOES have a setting to charge AGM batteries.

For me, these three primary reasons outweigh and justify the higher cost of AGM's.  In August, 2010, Two Sea Volt Dual Purpose AGM Group 24 batteries were purchased on sale from West Marine for about $40 more per battery than West Marine's comparable flooded cell dual purpose batteries.  A group 24 AGM is 14 lbs. heavier than a flooded cell group 24, and has a longer warranty. 


Gell Cells

Boating Magazine, in their September 2010 issue, discussed the various types of batteries and their pros and cons.  They described Gel Cells as made with many thin plates of lead and calcium, coated with a waxy or gel-like electrolyte and packed tightly together within a sealed case.   The article said Gel Cells are ideal for pure deep-cycle duty, but less than ideal as starting batteries and not as rugged as AGM's.  Maintenance free, these batteries cannot gas off electrolyte, and cannot leak even if the case is cracked.  Annual removal, cleaning, and lubrication of terminal connections is recommended with Gels.  Very specific charging profiles are required for Gels.  Gels have relatively low resistance to vibration and low cranking voltage.  The article rated Gels below AGM's for use in boats.


Boating Magazine, in their September 2010 issue, described AGM batteries as made with a pasty electrolyte bonded to plates pressed between an electrolyte-impregnated glass mat in a sealed case.  These batteries cannot spill acid, even if the case is cracked, and won't shed needed plate material when subjected to vibration.  Maintenance free, these batteries cannot gas off electrolyte, and are faster to recharge and provide more power in a smaller footprint (than flooded or Gells, I assumed) .  If isolated from current requirement, the article states that AGM's need no charging during storage.  (Wow!  If true!).  They do have specific charging requirements when charging is eventually required, (other than from the engine's alternator).  Because AGM batteries don't "cold creep", annual removal and cleaning of the terminal connections may not be necessary.  AGM's can be heavily drawn down without damage.


         AGM batteries are the latest step in the evolution of lead-acid batteries, (newer than Gells). The charging profile for AGM batteries is close but not exactly like that required for flooded cells.  Some web sites advise that a flooded cell charging profile can be used. No equalization charges are usually needed with AGM's. A downside- Once or if an AGM battery gets fried, the battery is impossible to revive. AGM's have much higher charge efficiency. Flooded cells convert 15-20% of the electrical charge energy into heat instead of potential power, Gells lose 10-16%, and AGM's lose as little as 4%. Flooded cells can lose up to 1% per DAY, (another source says about 4% per week at 80 degrees F) due to self-discharge, but AGM's lose only about 1-3% per MONTH.

AGM's should last longer than flooded cells.  West Marine warranty for AGM's is 18 months free replacement, 5 year pro rated versus 12 months/3 year for flooded cells. Because of the differing charging profiles required by flooded, Gell, and AGM's, ensure that your charger is capable of simultaneously providing different charging profiles if you are using mixed battery types.  If your charger cannot do this, then ensure that your charger can provide the charge profile required by the type of batteries you have, and do not mix the types of batteries used.
         The popular Optima batteries are AGM types.  Optima's  require different battery hold down hardware in boats and may present height problems in typical Campbell's.