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According to Wikipedia article lead-acid batteries are used for running submarines propulsion engines. Submarines are used by the military and the military can afford very expensive toys. Lead-acid batteries are cheaper, but have much worse energy density than say Li-Ion batteries (here goes a table with characteristics and energy density is a very important factor for a submarine battery - there's so little extra space that even people taller than certain height are not selected to serve on submarines.

What's so good in lead-acid batteries that they are preferable for submarines even with their lower energy density?

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    \$\begingroup\$ This is just a guess, but 1: The energy storage requirements are large so everything else would be much more expensive. 2: They are a tried and true technology that the people are trained on and know how to handle. 3: I wouldn't be so sure what exactly goes into newer subs regardless of what Wikipedia or anyone else says. We know that newer subs are nuclear generators so may not use batteries much or at all. \$\endgroup\$
    – Olin Lathrop
    Commented Dec 13, 2011 at 16:27
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    \$\begingroup\$ @OlinLathrop - while other battery technologies have probably been tried in high performance subs, lead acid batteries certainly overlap the usage of nuclear plants in subs; for one thing, it takes a lot of time and power to get the reactor re-started if it must be shut down. They generally carry diesels for backup too - but might not be able to ventilate to the surface to use them. \$\endgroup\$
    – Chris Stratton
    Commented Dec 13, 2011 at 16:54
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    \$\begingroup\$ It is generally worth taking wikipedia with a grain of salt, doubly so when it comes to military technology. \$\endgroup\$
    – ObscureRobot
    Commented Dec 13, 2011 at 19:01
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    \$\begingroup\$ What ObscureRobot said, military subs are pretty high up the list of top-secret things and pretty major factors in the arms race, anything anyone thinks they know is probably either wrong, or at least 20 years out of date, more likely several generations of development plus a few years. \$\endgroup\$
    – John U
    Commented May 27, 2014 at 13:47
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    \$\begingroup\$ Good Li-batteries are a product of the last 20 years, while most of the subs in service are older than that. \$\endgroup\$
    – pjc50
    Commented Jul 28, 2015 at 21:24

7 Answers 7

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Unlike surface vessels, submarines have to be able to sink. Every cubic foot of air space in a sub must be counterbalanced by almost 60 pounds of weight for a vessel to be able to submerge, and many submarines have a significant quantity of ballast for that purpose. Lead acid batteries have much less energy per unit mass than lithium-based batteries, but their energy per unit volume is pretty respectable (nb: something seems a little odd with that Wikipedia table; lead acid batteries weigh so much more than LiIon per unit volume that the difference in volumetric energy density should be much less than the difference in mass energy density). If one were to replace the batteries in a sub with magical batteries which stored the same energy and took up the same space, but weighed almost nothing, it would be necessary to add ballast to make up for the loss of weight (reducing the volume available for other purposes). It may well be that on some diesel subs, the batteries weighed more than ideal, and thus the weight of batteries was a limiting factor (rather than volume), but nuclear subs have much smaller stored-battery-energy requirements than diesels.

Also, lead acid batteries have more of a proven history of not going up in flames than do lithium-ion batteries. A submarine is not a good place to have things that may spectacularly catch fire.

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    \$\begingroup\$ They might not tend to burn, though lead acid batteries have a famously nasty habit of creating chlorine gas if flooding seawater reaches their electrolyte, and can release explosive-hazard hydrogen by themselves. \$\endgroup\$
    – Chris Stratton
    Commented Dec 13, 2011 at 16:59
  • \$\begingroup\$ @ChrisStratton: I hadn't heard of the chlorine problem (what would be reduced to balance the oxidation of 2Cl- to Cl2? I would think the Na+ would want to remain Na+). I can see that flooding seawater could be a problem if the batteries are in the lowest part of the vessel (which they likely would be given their purpose as ballast). \$\endgroup\$
    – supercat
    Commented Dec 13, 2011 at 17:17
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    \$\begingroup\$ @Majenko: Don't forget Murphy - gassing would surele happen when it was least needed and expected. \$\endgroup\$
    – sharptooth
    Commented Dec 14, 2011 at 6:35
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    \$\begingroup\$ Well, suppose I'm selecting batteries for a diesel-electric submarine. If I have batteries with better volume energy density it means I can have more energy in the same volume and if I need extra weight I could just add some lead blocks - they are inert and have very high density and can be positioned anywhere in the submarine unlike batteries that require maintenance and have lots of positioning requirements. \$\endgroup\$
    – sharptooth
    Commented Dec 14, 2011 at 6:39
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    \$\begingroup\$ @Majenko - "I would think that if the sub were filling up with sea water they'd be happy to be gassed before drowning." If the flooding is not instantly catastrophic, crews will be working hard to stop it, and have been known to do so successfully. It's hard to keep working in a chlorine atmosphere. See Wilfred Owen's "Dulce et Decorum". And no, chlorine asphyxiation is not better than drowning - it's slower, as the lungs gradually fill with fluid. \$\endgroup\$
    – WhatRoughBeast
    Commented Jul 28, 2015 at 21:05
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Lead Acid batteries have been around far longer than most alternatives - there were no lithium batteries when submarines relied so heavily on batteries.

But lead acid batteries also tolerate abuse quite well.

The Wikipedia article on the Royal Navy's first submarine, HMS Holland illustrates this.

Built in 1902, HMS Holland sank in 1913 while under tow to be scrapped, and was raised almost 70 years later, in 1982. As the article notes...

It is worth noting that the original bank of batteries, recovered with the wreckage, were provided for testing to the original manufacturer, Chloride Industrial Batteries Ltd based in Swinton, Greater Manchester. Following the initial clean, the lead batteries were recharged and found to be in good working order.

Pretty impressive, IMO.

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  • \$\begingroup\$ I love stories like this. Nice find. \$\endgroup\$
    – user98663
    Commented Sep 14, 2016 at 12:07
  • \$\begingroup\$ I know it's a Wiki story but I remembered an article about it (in an IEE journal) at the time. \$\endgroup\$
    – user16324
    Commented Sep 14, 2016 at 12:40
  • \$\begingroup\$ Nowhere in that article do they state the type of battery. They could have been iron nickel \$\endgroup\$
    – Dan D.
    Commented Sep 14, 2016 at 22:29
  • \$\begingroup\$ The 1980s article I remember confirmed they were lead acid. In any case, Edison only patented Ni-Fe the year HMS Holland was launched, while lead-acid had been around for over 40 years. \$\endgroup\$
    – user16324
    Commented Sep 14, 2016 at 23:42
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My husband served on R.N subs, and was forced to retire after a leak,these are surprising common, saw seawater enter the battery compartment, bottom of the sub as you guessed and with crawl room only, which released chlorine gas. The result was himself and the C.P.O both having their working careers finished permanenty after dealing with the leak. Lithiun Ion batteries however do have a alarming tendency to combust, especially with a sudden jolt, hence attempts by some of the most advanced sub builders like the japanese, looked, trialled, and dropped like stone.

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When you surface in a diesel sub & fire up the diesels three most important things to do:

  1. Post a lookout or 3

  2. Pump up your high pressure air tanks.

  3. Fast charge your batteries

Lead acid will take this punishment (with gassing). Lithium blows up

If you don't get jumped, float charge is OK. You may now top up the lithium batteries over 6 hours. By then, daylight is coming. Dive. You can then send guy with acid burns on his clothing, to top up the lead acid batteries with distilled water. Can't do a dammed thing with lithium, except replace a dud cell

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  • \$\begingroup\$ +1 "except replace a dud cell" which might not be that easy if you do not have spares and are half a globe away. \$\endgroup\$
    – Trevor_G
    Commented Oct 20, 2017 at 16:04
  • \$\begingroup\$ No. If detection is a concern, you don't surface to charge, you snorkel - they figured that out around 1943 when radar started to become an issue. \$\endgroup\$
    – Chris Stratton
    Commented Oct 20, 2017 at 16:50
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Li-Ion batteries are superior in terms of energy density, but like Lead-Acid batteries (chlorine and hydrogen gas danger) they have problems.

Thermal runaway in the main has been contained by the stack housing and battery management system, but the gasses given off during cell melt down are apparently very toxic.

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    \$\begingroup\$ In addition lead-acide batteries are extremely well understood technology. We know how long they last, they're rugged and generally have no big suprprises. Li-ion is not that well understood, and sometimes do have unforeseen properties. \$\endgroup\$
    – vidarlo
    Commented Oct 20, 2017 at 11:49
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Good answers here. Here are a few more points to chew on.

Batteries in submarines are wired up in an array, or series parallel connections. With the robustness of lead acid batteries this is not particularly problematic.

However, with more modern batteries that are much more sensitive to temperature effects especially during charging, it becomes more and more difficult to have the whole array operate safely as you increase the array size. Each battery needs to be monitored individually during charging. That significantly decreases the reliability of the whole.

Further, a failing battery in the array can quickly be driven into a dangerous condition by the remaining batteries. Special measures need to be in place and effective to deal with that. Again, down goes reliability.

Energy density, although seemingly a good thing, it is also "a double edge sword". If you can get all you power from something the size of a shipping trunk compared to a room for lead acids, that is all well and good. However, now you have to extract and get rid of the heat that is generated in that battery pack. Being that much denser means you have much less surface area and that makes it a more difficult proposition.

One more thing. One of the criteria of military anything is serviceability. Lead acid batteries are everywhere. If need be, a sub crew can scrounge some batteries from trucks and the like to do a quick repair, and set to sea again. Finding exotic batteries in some atoll in the middle of nowhere.. not so likely.

As for chlorine gas release. Yes that can be an issue with lead acid batteries but it is a small risk compared to chain reaction of exploding high tech batteries. The battery compartment can be gas sealed, the crew is trained on the use of gas masks, and gas leak sensors give plenty of warning to allow the commander to perform an emergency surface procedure if he deems that is safer than the alternative. Yes it's nasty stuff, but of all the risks our intrepid submariners endure, it is one of the less likely ones to affect/kill them.

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  • \$\begingroup\$ There are plenty of articles indicating that some of the most modern subs do use lithium batteries. \$\endgroup\$
    – Chris Stratton
    Commented Oct 20, 2017 at 17:15
  • \$\begingroup\$ @ChrisStratton yup, I am sure there are. It doesn't change anything I said though. \$\endgroup\$
    – Trevor_G
    Commented Oct 20, 2017 at 17:18
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Energy density is not the only measure of performance. Lead acid batteries have a good ability to supply enormous current without affecting voltage so much. This is important in rotating equipment (such as propulsion), and many other electric/electronic devices.
The other advantage is obvious....where many industries are looking to create light weight batteries, a submarine needs a huge amount of fixed ballast to submerge, and lead acid batteries are a no-brainer from that perspective.

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  • \$\begingroup\$ It's a bit questionable if peak power is actually a concern - when you have enough battery for hours of cruising, peak sprint may not be that high a draw per actual cell. And unlike say an E-bike hub motor (where lithium cells are used), you don't really have huge starting torque requirements. That said the other battery technology that seems to have actually been used was nickel cadium, and that is famous for supporting high peak demands. \$\endgroup\$
    – Chris Stratton
    Commented Apr 1, 2019 at 18:28

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