We lived and died with our battery. It was the altar, and we were the acolytes. The skipper was just the oldest acolyte.
In 1970, a week after I reported to USS Odax, a conventional submarine, we went into the shipyard to get a new battery.
John Paul Jones's ships were built in a Navy Yard. Oliver Hazard Perry's ships were built in a Navy Yard. David Farragut's ships were built in a Navy Yard. Chester Nimitz's ships were built in a Navy Yard. Tojo and Yamamoto were defeated by ships that were built in Navy Yards. The Boston Navy Yard could still be using the same letterhead as in the eighteenth century, with a zip code added. But some bureaucrat(s) decided that the name "Navy Yard" was no longer adequate, and changed all the active Navy Yards to "Naval Shipyards".
We moved everything out of the boat. We put the sailors into barracks. We put the boat's offices into a funky spare office building at the shipyard. We sent most of our crew members to school for a couple of weeks.
The yardbirds came down and cut holes into our pressure hull. They took our old battery out, cell by cell, with a crane. Lots of riggers were required.
Riggers are the folks who move heavy things around. It is a legitimate skill, and the rigger's trade is as respected as any other skilled trade in an industrial facility.
At one point I walked around in the empty battery well, standing up straight. And I am 6'3" tall.
Then they brought a new battery down and began installing it. There were 504 cells. Each cell weighed perhaps 1,500 pounds. The cells were placed into the battery wells one at a time, carefully positioned. The positive terminal of one cell was connected to the negative terminal of the next with a piece of copper bus bar. A pre-measured amount of sulfuric acid was added to each cell as soon as it was in its final position.
When the cells were connected into four batteries of 126 cells each, there was very little clearance left for the boat's Electrician's Mates to slither on their bellies on top of the battery cells. Perhaps eighteen inches of vertical clearance was available atop the center rows of cells. The outer rows had less room for checking the connections, the vents, the temperature, the fluid levels, and the specific gravity.
Once the battery was installed, and the boat was reassembled, we started the tests. We measured, and we recorded with pencil and paper, the voltage of each of the 504 cells. We put dozens of sampling tubes at selected locations around the battery wells to sniff for hydrogen. We took the temperature of each of the 504 cells. We added distilled water to each of the 504 cells, until the fluid level of each cell was at just the right height. Then we started the battery charge.
One of those old locomotive diesel engines, in its submarine configuration, was rated at 1,600 continuous horsepower. Our direct current generators were limited to 3,000 Amps, though. So with a nominal battery voltage of 250 VDC we were limited to 750 kVA or 1,000 horsepower, per generator. We could put all four engines on line, putting 12,000 Amps into the battery, but that got a little too tricky sometimes.
When you start to charge a battery like that, the initial temperature is a critical bit of information. The initial temperature is the primary, essentially the sole determinant of the voltage above which the battery will evolve significant hydrogen gas as it is charged. We did not hesitate to charge the battery at 12,000 Amps, so long as the voltage was below the gassing voltage. And that voltage differed every time we charged the battery, so we marked it in grease pencil at the start of every charge.
In this case, with a brand new battery and lots of extra test equipment, we started the charge with several engines and we continued until the voltage was at TVG (Temperature-based Voltage for Gassing). Then we slowly backed off on one generator output to maintain that voltage. Let's call it 300 Volts. When one generator's output reached zero Amps, we disconnected it and secured that engine. When the final generator's output had dropped from 3,000 Amps to 1,200 Amps, we left it at that setting. At a charging rate of 1,200 Amps, the battery did not evolve enough hydrogen to be a hazard. Eventually, after several hours of charging, the battery voltage reached 340 Volts. When the battery voltage did not increase any for a two hour period, even while 1,200 Amps of charging current was flowing, the battery was considered fully charged.
Oh, yes. The hydrogen. Hydrogen at a concentration of more than four per cent in air is flammable. Hydrogen at a concentration of more than eight per cent in air is explosive. We set our limits at a hydrogen concentration of 2.5 per cent in our battery wells. And we watched it closely. Very closely.
After twenty hours of charging the new battery, we conducted the last round of tests. We identified the eight locations that had the highest hydrogen concentrations, and we mounted the permanent sampling tubes at those locations. And we identified the eight battery cells that were most representative of the 504 total cells, and we named those our "pilot cells". After that, we only checked out the entire battery, with 504 voltage readings, 504 temperature readings, and 504 specific gravity readings once every 28 days. Then we added water to each of the 504 cells and we gave the battery an charge that lasted an extra twelve hours. In between, we only took readings on the pilot cells.
Every four hours at sea or in port, except when we were connected to shore power, we monitored those pilot cells. When we were using shore power, we only needed to check them every 24 hours. To read the cells, an Electrician's Mate went down into the battery wells and slithered on his belly across the tops of the cells. He unscrewed the cap on each pilot cell, and he measured the height of the electrolyte. He measured the specific gravity of the electrolyte. He measured the temperature of the electrolyte. Then he climbed out of the battery well and he went to the master panel where he measured the voltage of each pilot cell.
All of this information about the electrolyte was used to calculate the "corrected" specific gravity of the battery. This final number was the one, the only measure that we had, in a dynamic operating environment, that told us how much stored energy we had left in our battery. This was the sacred "Gravity".
Once the gravity was calculated, the Electrician's Mate wrote it with a grease pencil on a status board in the control room, and the Chief of the Watch looked at it and nodded sagely, muttering "hmmms" and "umphs" under his breath. The Chief then respectfully reported the gravity to the Diving Officer, if we were submerged. The Diving Officer was expected to nod reverently as this information was passed along. The Diving Officer then yelled the gravity reading up to the Officer of the Deck (Submerged) in the conning tower. Three times a day, the Messenger of the Watch gravely reported the gravity to the skipper, as part of a formal presentation.
If we were running on the surface, then the Chief of the Watch simply called the Officer of the Deck (Surfaced) on the sound-powered telephone and told him the gravity.
A specific gravity of 1.265 indicated that our battery was fully charged, and that it stored 22,000 Ampere-hours of energy at 250 Volts. A specific gravity of 1.140 indicated that our battery was fully discharged, and that the warranty was void if we allowed the gravity to drop any lower. In our vernacular, these readings were pronounced "twelve sixty-five" and "eleven forty" respectively. Whenever the gravity dropped below twelve, the skipper and the exec were constantly asking about the gravity.
When the operation allowed, we charged the battery. Sometimes we got to charge it fully. Many times we just charged it as much as we could, stopping the charge just a few minutes before we submerged, so we could burn off as much residual hydrogen as possible before diving.
Fresh air, or air from the space that the people occupied, was ducted into the battery wells to ventilate the battery to keep the hydrogen concentration down while a battery was being charged. The exhaust air from the battery was ducted directly from the battery well to the engine intakes, so the hydrogen was burned in the diesel engines.
Whenever an officer, any officer, passed through the control room, even if only to get a cup of coffee, he asked, "What's the gravity, Chief?"
Whenever an officer prepared to assume a watch, whether as Diving Officer, as Officer of the Deck, or as the Duty Officer in port, his first question was, "What's the gravity?"
Whenever an officer got off watch and reported to the skipper that all was normal, the skipper asked, "What's the gravity?"
Whenever the officers were at a meal together, and the executive officer, or "exec", realized that he had not been paying close attention to the battery condition for the last couple of hours, he asked, "What's the gravity?"
When the in-port Duty Officer had to call the skipper at home on a Sunday morning to report that one of our sailors had been arrested for having too much fun on Saturday night, the skipper always asked, "What's the gravity?"
We worked the hell out of that battery for three years. We got compliments from our anti-submarine warfare forces for giving them the wildest, craftiest, most energetic opponent they had worked with/against in years. When we sold the boat to Brazil, all 504 cells were still in good shape.
At the reception after the ceremony in which USS Odax became S. Rio de Janeiro, I heard our (former) skipper ask our (former) Engineering Officer, "What was the gravity?"