This page was last updated on July 17, 2001.


Ah yes, batteries!  So seeming magical in their performance until the day you are unknowingly stranded with a dead battery bank.  What went wrong?  How do you avoid it?  How large should your batteries be?  And how should you set up the system for more efficiency, proper charging, and satisfactory capacity?

Well, I'm not going to answer all these questions in the specific sense--check out the resources on the battery charging page for more information on the specifics--they'll explain it better than I could.  What I will do, however, is pass along details of my own installation and the thought process behind it.  Later, once Glissando is in the water and being used, I'll report on the operation and success of the installed system.

First, I laid out what electrical equipment I planned to have on board, and totaled up the expected daily usage of the gear.  This is a worst-case scenario, and certain usages cancel out others for practical purposes.  For example, if the running lights are on, it is unlikely that the cabin lights are needed, and the GPS and instrument usage may be higher or lower depending on whether day trips or overnight trips are being made.  However, for the purposes of estimation, the totals are calculated without factoring this in.  There may be other usages, such as the bilge pump, AC usage through an inverter, etc., but these are either not estimated or are so insignificant that they were not factored in to the expected totals.   The additional capacity of the batteries is more than sufficient to take care of these small additional needs.

Device Power Usage (Amps) Hours Use per Day Total Draw
Cabin Lights (Halogen) .4 3 8 lights @ 3hrs=9.6 amps
Running Lights 3 8 24 amps
Masthead/Anchor Light 1 8 8 amps
Steaming Light 1 8 8 amps
Stereo 1 3 3 amps
Engine Starter 150 .02 3 amps
GPS/Instruments .75 5 3.75 amps

The total usage from the above chart is 59.35 amps per day.  Because the general rule is to provide a battery capacity at least double that of your expected usage, we needed at least a 120 amp-hour battery bank.  Plus, you want additional capacity since you shouldn't dray deep cycles batteries down lower than about 50% of full charge.  Of course, we wanted additional capacity to handle the inevitable additions that will occur over the years, plus the ability to go more than a day between engine charges.  In practice, I expect the actual usage will be even less than the above, especially since we don't plan on many overnight trips.  This means that the running light and steaming light usage can be effectively zeroed out.  

After much thought, research, pricing, etc., I decided to try a single house battery bank made up of two Trojan T-105 golf cart batteries.  These are 6-volt batteries, so two are wired in series for 12 volts.  The batteries have a rating of 220 amp-hours, which is excellent and comparable to an 8D 12-volt battery.  With 220 amp-hours available we should be able to do at least between 2 and 3 days between charges, using the available capacity between 50% and 90%.  With the added convenience of the installed energy monitor, we will always know exactly when charging is necessary.  It will be nice to be at anchor and not have to worry about charging the batteries every day.  The benefits to the golf cart batteries are many:  

  • Initial cost is substantially lower (about $65/battery = $130, vs. over $400 for the 8D)

  • The divided weight of the two separate batteries is manageable; an 8D is virtually impossible to move once it's in place.

  • Even if the 6 volt batteries have fewer discharge cycles available than  a gel or AGM battery, replacement is inexpensive enough that they still provide a better value for the power supplied.

  • It will be easy and inexpensive to double the battery capacity by purchasing two more T-105s, if such capacity is needed.

In addition to the house bank, I will also install a single engine starting battery, probably a traditional Group 24 automotive type.  Because of the regulation and monitoring system I have installed, the starting battery will automatically be isolated at all times, except when the engine is running.  This will prevent any possibility of the starting battery being inadvertently drawn down by house power during the night, and it will always be ready to start the engine.  This system eliminates the traditional useless 1-2-all switch seen so frequently and replaces it with an emergency parallel on-off switch to tap the house bank for the engine starting if  necessary for whatever reason.

I plan to install the two Trojans in the starboard cockpit locker, just aft of the galley bulkhead.  I'll locate the starting battery opposite to port.  Hopefully, this weight distribution will balance out the icebox (on the port side) when it's full of ice., to the extent necessary.  The batteries will be installed in custom boxes that are yet to be built, and connected into the electrical system as necessary.  I purchased the two T-105s and a midrange Trojan group 24 starting battery at Ed's Batteries in Westbrook, Maine.

To make installation easier, and to comply with all the various requirements for battery restraint and safety, I hoped to use one of the nice Blue Seas battery boxes.  I ordered one to fit two golf cart batteries.  However, without access from directly above (which would entail another large hatch in the cockpit seat, which I wish I had thought of adding when I had the chance) I just could not get the box to fit in the space available.  The curvature of the hull is too extreme in the cockpit lockers.  The batteries are not particularly large in and of themselves, but the box, with its molded channels and feet, was somewhat more cumbersome.  Try as I might, I could not get it to work.  Oh well.

I ended up constructing a pretty simple platform out of plywood.  I built one for each side--the starting battery, while residing in a standard Attwood battery box, still needed a level platform on which to sit.  The platform for the house batteries consists of a piece of plywood cut to fit the two batteries side by side, with a 3" high edge banding of plywood all around.  The forward end of the platform rests on a cleat that is screwed to the aft galley bulkhead (or the forward locker bulkhead), and the after end features a plywood gusset that I shaped to fit the curvature of the hull.  Both ends are set in epoxy and bonded into place.  Later, I'll paint everything out with Bilgekote, but there's no time now.  It required some gymnastics to be able to reach the forward bulkhead to attach the cleats--it's just too far to quite reach without hanging upside down and half in the locker.  To make the job easier, I predrilled for screws every couple inches--to make sure there would always be a screw hole where I wanted it--and applied double-stick tape to the back before reaching up through my cockpit sole access hatch to press it into place (I found the access was easier for this step through the hatch, rather than through the top of the locker.  I tried it both ways...).  Then, I drilled a pilothole through the pre-drilled holes into the plywood of the bulkhead, and, taping a screw to the end of my drill driver, I installed screws.  A simple job made difficult by poor access...isn't that what boats are all about?

The starting battery platform is similar, but only features the edge banding on two sides.  I left the aft end open to allow me to slide the box in and out, and the box is restrained by its own strap anyway.  Clearance is very tight beneath the cockpit seat and sidedeck drain hoses on both sides.

I made up a pair of jumpers between the two 6-volt T-105s.  Of course, stupidly, I forgot that you only need one jumper for batteries in series--the positive lead from the first battery gets connected to the negative lead of the second, while the main ground is attached to the negative of the first battery, and the main feed is attached to the positive of the second battery.  I hooked them up wrong at first, and was sorely disappointed when there were no signs of life in my electrical system.  After some head scratching and a major "DUH!" heard 'round the land, I figured out my problem and quickly changes the cables around as necessary.  The system sprang into life, happily, and I continued kicking myself in punishment for my dumb move.  I held the batteries down with some heavy-duty rubber bungees, and covered the positive terminals with rubber boots for protection.

For more information on the electrical system in general, and the charging/monitoring system, please view these links:

Electrical System Wiring

Charging, Regulation and Monitoring


Glissando, Pearson  Triton #381

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