New batteries, August 2015

The project that kept growing...

We decided that our batteries, bought in January 2011, were shot and needed replacing. Of course, we first 
agonized over whether there was any way to salvage them, spending hours charging them, "equalizing" them 
(don't ask!) and even removing them and dropping them on the dock to remove sulpher from the plates, then 
rolling them around to mix up the acid and rejuvenate them No dice. They just didn't produce power, and 
lost their charge pretty quickly.
These were 12-volt Trojan batteries, six of them, configured into two separate banks of three batteries 
each. This configuration provided us redundancy and safety – we could throw a switch and use just one of 
the two banks, or use them all. Now these are not ordinary batteries – they are deep discharge (read: 
ka-ching), and manufactured by Trojan, the Cadillac of batteries (double ka-ching). We'd bought them in 
Panama and gotten a pretty good deal on them, but kind of felt they should have lasted longer than they 
So the question was what to replace them with?
    · New Trojans, which cost a lot more here in Mexico?
    · The local brand, the quality and durability of which is unknown? or
    · 6-volt "golf cart" deep discharge batteries?

This last option was tempting, and one we'd considered before. Golf cart batteries are specifically designed 
to take very deep discharges. After all, golf carts are used all the time by golfers who cheerfully run the 
batteries down until the cart won't move. So whereas Trojan batteries can withstand, say, 30 really deep 
discharges, golf batteries can tolerate hundreds. Also, they are readily available and any brand will do. 
And because they don't have the designation "marine", the ka-ching noise is muffled somewhat.
So, why this wasn't this decision a no-brainer? The problem had nothing to do with the batteries themselves; 
it had to do with our boat. Our battery banks are located in two fiberglass boxes in the starboard lazarette 
(a very large locker alongside and under the cockpit). The boxes sit under a set of lovely teak grates, on 
top of which we store lots of gear. Each box is the right size to hold three 12-volt batteries comfortably, 
so we reckoned we should be able to fit three 6-volt batteries in their place, because 6-volt batteries have 
the same footprint as 12-volt ones. 

BUT, the 6-volt batteries are 1/2" taller than the 12-volts, and the battery boxes were too short. Could we 
add an inch of fiberglass to each box? But then, because the boxes would be taller, the built-in supports 
for the teak grates would be too low, and the grates and all the gear on top of them would be sitting on the 
battery boxes instead of the supports that were designed to hold them. So the supports would have to be 
raised, as well. 

Of course, WE couldn't do this, but we knew a worker who could: Lalo, the same guy who made all the new 
headliner panels for our cabins. So we contracted the work with Lalo, to be done while we were in the US in 
When we returned we found that, due to a misunderstanding, the work hadn't even started. But Lalo got right 
to work as soon as we were back, and had the newly extended boxes done in 2 days. Lalo and Rob took the 
modified boxes to the battery store and tested the fit with three 6-volt batteries. The new box height was 
perfect, and the "U" shaped openings Lalo had cut above the holes for cables in the ends of the boxes looked 
as if they would accomodate the higher exit points of the cables perfectly. On the other hand, it seems that 
the footprints of 12- and 6-volt batteries are not EXACTLY the same. Whereas the 12-volt batteries had fit 
into the boxes with a bit of spare room between them, the 6-volt ones were tightly packed! But fortunately 
they did fit, so we ordered the batteries for delivery the next day. Meanwhile, Lalo went to work on raising 
the supports for the teak grates, a job he completed in another two evenings. 
While Lalo was fiberglassing we had time to plan out how to connect all of these batteries. Two 6-volt batteries would be connected in series to form a conceptual 12-volt battery. The remaining 4 would also be connected in series to form two 12-volt batteries, and those batteries would be connected in parallel to make a second bank.
(Still with us, here?) After trying to draw diagrams of this wiring scheme that didn't look like spaghetti and didn't short out at least one of the 6-volt batteries, we finally went to the internet for a "standard" diagram of 6-volt batteries connected into a bank of 12-volt ones. The complicating issue for us was that each of our boxes holds three batteries, so one of the four 6-volt batteries forming the second bank would have to be in a different box from its mates. We were going to need to fabricate some new connecting cables, for sure! Amazingly, the nearby marine store had the cables (ka-ching) and we already had the lugs. Cutting and crimping would be the challenge. We told our across-the-dock neighbors. One loaned us his grinder with a cutting wheel; the other loaned us a nifty hand-held hydraulic cable crimper, both of which made the job much quicker and easier. (Our usual method involves a vice and hacksaw, vice-grip pliers, a bolt to form a groove in the lug, and repeated vice-grip adjustments until our hands are too tired to squeeze anymore, at which time we declare the crimp to be done.)
We spent a morning carefully measuring and cutting cables, then connected all the batteries, closed the 
boxes and put the grates on. Whoops! Despite our careful measurements, the grate supports were not high 
enough, and one grate sat on top of the box. Reluctantly, we called Lalo and asked him to add more height to 
the supports. He graciously came that evening after his regular job and did the work quickly and 
Did we mention that while the batteries were disconnected, we had no 12-volt electricity on board? We are at 
a dock, so we had "shore power" which charges our phones and computers and runs our air conditioner (else we 
would be completely melted away), but we had no running water, reading lights, stove or refrigeration for a 
couple of days. As soon as we had the first two 6-volt batteries connected, we got power restored. Of course, 
we had to disconnect and remove the batteries and box again while Lalo re-did the grate supports, but that 
was a fairly quick process.
At last, we did the final check of the boxes and all the cable runs. And discovered...

The box tops didn't fit. Because of the extra height of the 6-volt batteries, the cables coming through 
those U-shaped holes don't actually sit all the way down in them, but come over the edges of the batteries. 
The box lid needed to be cut away so that it didn't press on the cables. Another messy morning's work with a 
saber saw and file, and finally, we have new batteries!
Oh yeah, the project wasn't quite done, because all of that gear that we removed from the lazarette which 
was piled in the cockpit and aft cabin still had to be put back. 
There's always tomorrow...