Engine Start Battery Research

[Mike]

I did a lot of work researching different battery types for my engine-start application.  The following conditions were analyzed.

1. Form Factor - 8D, 4D, G31, G27, and G24
2. Chemistry - Flooded, AGM, LiFePo - Since this is engine start, I ignored Li
3. Cold Cranking Amps (CCA) - 1100 - This is the 0 degree value
4. Marine Cranking Amps (MCA) - Ignored - This is the 32f degree value and not all batteries had this rating
5. Amp Hours (Ah) - 200-300 - Basically the amount of reserve power required to start multiple engines.

I went through all of the battery options I could find at Fisheries Supply.  I also compared a few others from West Marine and online sources but it turns out that most batteries end up showing similar results.  A few exceptions with higher performance batteries in the smaller form factor.

I first calculated the values for a single battery, and then later in my evaluation I decided to calculate the values based on combined batteries.  See the following chart (crude that it may be, and some generalization):

The green line in the middle indicates my most important attribute, CCA.  I needed to find a battery that could easily crank both engines and 1100 CCA is the value I found works well for the TAMD63.  As you can see, there are only a few single batteries that will meet this important spec.  Of course Navigator installed 8D flooded batteries back when the boat was new.  These work fine and I can see why they chose this format.  However, one battery in the middle stuck out, and it's the Odyssey G31.  It seems to have the CCA value necessary to turn the engine and get it started.  The only other contender was the 4D AGM, which also seemed to meet the spec.  But one thing had me worried, and that's the G31 might not have enough power, after a single start, to get the next engine cranking.  So, I looked at the Ah rating for both batteries.

1. 8D = Around 255 Ah
2. 4D = Around 210 Ah
3. G31 = Around 100 Ah

Based on these facts, I decided a single G31 battery would not cut it as a single engine start solution.  But one per engine would work fine.  But what about the generator?  Hmmm....

Also I am no longer considering Flooded batteries, so here's the same chart with AGM values.  I've also added a West Marine option and a G24 Odyssey I found at Fisheries today.

 

To be continued...

 

[Mike]

Needless to say, I started looking around for a battery box setup for G31 batteries.  Nothing.  I mean nada.  I even tried driving over to Fisheries and working with the guys to see if they had something to dual G31's into a single box.  We came up with nothing.  The G31 batteries are about an inch too wide to fit side-by-side in a box.  I went back home and did some Internet searching and came up with the same result.  However, over at the hull truth site I did see a single post from a guy who found a solution.  The company Custom Roto Molding, Inc seems to have a custom built solution.  Their boxes are reasonably priced but takes several weeks to have custom made.  I have no affiliation with this company and have only read about them.  But alas, I need more than 2x G31 batteries (can't forget the generator).  It is certainly an option to buy two Custom Roto boxes and install 4x G31's.  If you look at my chart above, it will more than suffice.

However, I wasn't done yet!  If you remember, based on experience from my previous battery setup (only a single 8D starting all three engines reliably), I decided this would be my 'standard' when choosing new batteries.  So I continued to calculate it.  Looking at that same chart, I discovered the following configurations will absolutlely work well for a triple engine start solution:

1. 1x 8D
2. 1x 4D (would need RL verification)
3. 1x G31
4. 2x G27 (not Mastervolt)
5. 3x G24

The above list works for a single engine.  Since the G27 is only 3/4" smaller I ignored this form factor.  So, my last option was to look at the 3x G24.  Specs seem fine, and it meets both my CCA and Ah requirements.  But is there a box for these batteries?  There sure is!  3x G24 batteries will fit into a single 8D box.  Here's proof.

 

Score!!!  This is a photo of three Odyssey G24 batteries fitting into a single 8D box.  Let's weigh the advantages and disadvantages.

Advantages:

1. Lighter batteries to move - Each battery weights significantly less than a single 8D or 4D, of course
2. Clean box solution
3. Ah is good - Combined approx 240 Ah
4. More CCA than required - Combined CCA approx 1,980

Disadvantages:

1. Jumper Cables - This setup needs to have custom jumper wires built (PITA)
2. More points of Failure - As with all battery setups, corrosion on the terminals, shorts, etc
3. Cost - Purchasing three batteries does cost more money, labor, and cabling

To be continued

[Mike]

So what about the overall cost?   If you look at the chart, you'll notice that multiple batteries is more expensive than going with a single 8D or 4D.  My round figure is approximately $1000-$1200 per battery.  Since I am going with a redundant system, my budget is around the $2,500 mark.  Let's look at each solution (in today's dollars):

1. 2x 8D = $2,238 - Two batteries, two 8D boxes, 312 total lbs
2. 2x 4D = $1,892 - Two batteries, two 4D boxes, 248 total lbs (will it work long term?)
3. 3x G31 = $1,968 - Three batteries, two custom boxes, 225 total lbs (will it work long term?)
4. 6x G24 = $2,682 - Six batteries, two 8D boxes, 342 total lbs

There's a lot of factors to consider and I've basically rounded this out to a final answer.  The original Navigator design, using an 8D battery, is the best option.  Although this battery is heavy, it's got the raw reserve power and simplicity.  Other options are certainly capable but they are either difficult to find boxes, more expensive, or complex.  Options 1 and 4 are known and proven solutions by many Navigator owners.  Option 2 and 3 are certainly possible, but there is a question if these batteries will hold up long term or if they will have enough to start all three engines reliably for years.  Are you willing to toss money at something that 'might' or 'might-not' work?

If you have the resources to move the MASSIVE 8D batteries around, it's certainly the most efficient and simple way.  If you don't have any 'helpers' around, the smaller batteries will give you the capability to move these on your own.

PS:  You probably noticed I ignored flooded batteries.  I hate this battery technology so much that I will never use another flooded battery in my boat.  😉  Dangerous off gassing, acid on your clothing, acid smell, and watering them every quarter..  need I say more?  Ok sure, they cannot be fully discharged and literally only provide you with half of the spec listed on paper.  Ugh, how bad.  Only advantage is they are cheap.

PSS:  I also want to note that I am going to use boxes.  It is NOT required to mount an AGM battery in a box, which is only required to catch acid spills.  I've decided to use boxes anyway because I want to stack things on top of my batteries and eliminate any possibility of a short circuit when I'm working in the engine room.  Remember, batteries do need to be held down so it cannot move around.  Using a battery box makes this a lot easier to manage.