I have two lead-acid batteries of the plate type, 12 V/100 Ah each, used for an inverter. I want to store these batteries for a year or two in a disconnected state.

A friend of mine told me it's better to drain the batteries of the liquid they contain and store the liquid separately and then when the time comes to reuse the battery to fill the liquid back into it.

  1. Is this sound advice, are there any demerits to this, will this cause damage or degradation to the batteries when kept in this state for a long duration without any electrolyte in it?

  2. Is there a better way to store lead-acid batteries than the above in a disconnected state for a year or two?

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    \$\begingroup\$ I would get a maintenance charger instead of draining the battery. \$\endgroup\$
    – Kyle B
    Nov 7, 2022 at 15:10
  • \$\begingroup\$ @KyleB have never heard of that term before, although I do know about a battery charger, will look it up. \$\endgroup\$
    – Anchovy
    Nov 7, 2022 at 16:55
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    \$\begingroup\$ Must be a smart maintenance charger with temperature compensation. Letting it go completely dead, even from self-discharge, will destroy it permanently. Overcharging and drying out the battery will also damage it. \$\endgroup\$
    – tomnexus
    Nov 7, 2022 at 17:11
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    \$\begingroup\$ this is an XY question ... you are asking about your solution to a problem, instead of asking about the problem itself \$\endgroup\$
    – jsotola
    Nov 7, 2022 at 21:24
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    \$\begingroup\$ anecdotal: Been there, done that, would not recommend doing it again, the bit remaining acid dried out and left sulfates that partially destroyed the plates. \$\endgroup\$
    – PlasmaHH
    Nov 8, 2022 at 21:32

5 Answers 5



First, the theory:

Dry-charged batteries are not prepared by flooding them, charging and draining them afterwards.

Instead, the plates are press-formed with the approximately proper chemical composition corresponding to a fully or a partially charged battery. In some cases, the plates are formed as a fully depleted battery (they are dry, but not charged and the charging is expected to happen after flooding them).

In either case, there was no even a smell of acid in the batteries when they were shipped.

Absorbing the useful comment from @Pete Becker: "they weren't transported in a drained condition, they were transported in a never-been-filled condition"

Why it was done:

  • Dry batteries were considered safe cargo. One has to still transport the acid, but it is only 10% of the weight (or even less if you carry it concentrated) that has to be transported under the regulatory rules.
  • Shelf life wasn't great. Storing batteries dry improved it to a great extent.

Why it is rarely done these days:

  • Battery bodies improved a lot. Polypropylene is much better material than bakelite. Caps with valves, etc... Breaking or spilling is much less of a concern.
  • Shelf life and self-discharge improved as well, thanks to the technology advance. Today a sealed maintenance-free battery generally has the same shelf life as its dry counterpart from the past.
  • The factory can test 100% of the production before shipping. Less RMA, oh, yes!
  • Finding someone to deal manually with sulfuric acid is harder these days. Arranging a workplace for them is more expensive as well (see below about the purity).

Dry lead-acid batteries are now only used when compliance with an obsolete regulation is needed.

Some retro-car enthusiasts use them as well. They have their own reasons. Most of them generally try once.

What WILL (not may, but will) go wrong if you go on with your plan:

  • About a half of the electrolyte will stay soaked in the plates and the plate separators. The parasitic chemical processes will continue almost as usual. Getting these things dry is not trivial. I bet you can drain the electrolyte and still get some 30% of the electricity out. Some early special-use batteries got such numbers specified for operation in bottom-up state.

In short: you get no storage benefit.

  • There is always some sludge at the bottom of the cells of a flooded battery, even in fairly new ones. This is a product of the plates decomposition.

You really, really don't want particles from the positive plates on the negative ones and vice-versa. The plates are not only lead/lead oxides/lead sulphate. They contain additives and the positive and the negative plates contain different additives that are quite counter-productive at the wrong place. They promote self-discharge with hydrogen emission. For an older battery, the sludge can be enough to happily short the plates. In this case, the battery can explode.

You may think of draining the battery from the bottom, using some tube? Your tube has to be less than ~2mm (or less, depending on the battery type) in diameter or it will scrub some active mass from a plate.

Submarine batteries are serviced like this, but they have the tube(s) installed from the factory and they are constructively different in the first place.

  • Storing a battery acid outside of a battery is a challenge both in regard to safety and purity.

The battery acid is not immediately dangerous to humans (well, keep it away from your eyes and mouth), but it is corrosive to a great variety of materials and does impressive things to cotton-based clothes.

And then, the purity. Allowing even trace amounts of some substances (e.g. iron) into the battery can kill it rather quickly or at least lower its parameters a lot. Glass container is OK. Glass container washed with tap water is not. You need deionized water for the final rinse. Polypropylene or polyethylene is OK if it is food grade. etc, etc...

In short, top up your batteries with some sane charger and leave them in the basement. Or wherever. Colder is better as long as it is not below, say, -5C.

Most batteries survive a year or two with this storage strategy.

  • 1
    \$\begingroup\$ @Anchovy the sludge from the bottom is mixed from the two types of plates. It will contaminate both positive and negative plates indiscriminately. \$\endgroup\$
    – fraxinus
    Nov 8, 2022 at 19:55
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    \$\begingroup\$ In regard to transporting them dry: it is too 1980-y. Batteries were transported dry only when new and dry from the factory. This was considered safer and the shelf life was somewhat more. The mass consideration is moot since 25kg battery needs 2 or 3 kg electrolyte and one has to transport the electrolyte anyway. Well, it is better to expand the answer. \$\endgroup\$
    – fraxinus
    Nov 8, 2022 at 19:59
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    \$\begingroup\$ @Anchovy -- they weren't transported in a drained condition, they were transported in a never-been-filled condition. \$\endgroup\$ Nov 9, 2022 at 13:27
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    \$\begingroup\$ @PeteBecker This is the exact, 100% right explanation, "they weren't transported in a drained condition, they were transported in a never-been-filled condition" +100 \$\endgroup\$ Nov 9, 2022 at 13:41
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    \$\begingroup\$ @WayneConrad sorry, but no, I did not serve on a submarine. My interest in submarine batteries came from the battery side and not from the submarine side. Anyway, they are just oversized traction batteries with tubular electrodes and some interesting stuff dealing with scale-factor problems and in-place servicing (e.g. cooling system, electrolyte mixing system, electrolyte sampling tools, etc...). Anyway, my knowledge about them is somewhat dated, I learned these things some 20 or 25 years ago. \$\endgroup\$
    – fraxinus
    Nov 10, 2022 at 9:45

Yes, this is possible.

In fact we had deliveries of hundreds of dry-charged batteries and separate deliveries of the acid / liquid to fill them with. Guess who, as an apprentice, got to mix the acid to the correct SG and fill batteries.

They were transported like that as the liquid is heavy and more batteries can be carried. Also, if there was an accident there is no liquid running around.

So, yes, storing batteries dry is possible. But if the plates are weak or damaged it might not turn out well.

Oh, and if you even think about trying this then make sure you have all the safety gear.

  • 6
    \$\begingroup\$ Do you think it's OK to remove the electrolyte again, or is that a once-off process? \$\endgroup\$
    – tomnexus
    Nov 7, 2022 at 17:09
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    \$\begingroup\$ @tomnexus: I expect that those "dry charged" batteries were manufactured with the plates having the proper chemical composition for a charged battery, but never saw acid until it was added by the seller. I don't think you could get a used battery dry enough to prevent self-discharge and sulfation. \$\endgroup\$ Nov 7, 2022 at 17:23
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    \$\begingroup\$ Does this process work only for new / unused batteries, or can it be done for used batteries too? Also is it necessary to fully charge the battery before performing this procedure? \$\endgroup\$
    – Anchovy
    Nov 7, 2022 at 19:04
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    \$\begingroup\$ @Nelson Although it may feel so to laypeople, sulphuric acid (even concentrated, which the electrolyte is not) is not the devil. As far as chemicals go, it's on the fairly safe end of the spectrum: yes, it can burn you and anything else if you spill it, but it doesn't release any toxic fumes and it is neither flammable nor sensitive to shocks or light. Depending on the amount, any glass bottle or polyethylene container will do (no metal caps or anything!). Proper PPE is of course required. \$\endgroup\$
    – TooTea
    Nov 8, 2022 at 10:13
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    \$\begingroup\$ @TooTea good luck getting all of the electrolyte from the pretty much porous plates and separators. 1/3 to 1/2 of the electrolyte will stay soaked in. \$\endgroup\$
    – fraxinus
    Nov 8, 2022 at 14:41

A friend of mine told me its better to drain the batteries off the liquid that it contains and store the liquid separately and then when the time comes to reuse the battery to fill the liquid back into it.

If this was really a good, applicable, and recommended method then it would be indicated somewhere on the battery or in the manual/guideline. Besides, inside the battery there is basically an acid (the density might be lower compared to a bleacher but, still an acid).

A lead acid battery can be stored for at least 2 years with no electrical operation. But if you worry, you should:

  • Fully charge the battery
  • Remove it from the device
  • And store at room temperature

And, if possible, recharge it periodically (3 to 6 months).

After all that storage time, before first use, you should recharge the battery again.


A lot depends on your location. I lost several batteries by using a maintenance charger over the years. Since I was tired of changing batteries I got lazy and disconnect one of the battery leads in the car and then fully charged the battery. It was stored in an unheated garage for about 9 months (winter in Michigan), come spring I charged it connected it and drove away. This is the third successive year with this battery, no problems. This whole process takes only a few minutes and is a good excuse to clean the battery terminals.

Yes and the water levels did not drop. When the battery is not charging or being discharged no activity is created by the plates consequently no water is evaporated or driven off. The batteries are closed so nothing can escape to the atmosphere except via the vent caps.

The fact that you have to keep adding water indicates you are probably overcharging them. This would also explain short life cycles.

  • \$\begingroup\$ I somehow didn't get it, don't we need to periodically replenish the battery with distilled water? Did the battery stay hydrated for the entire duration of 9 moths without getting dry? \$\endgroup\$
    – Anchovy
    Nov 13, 2022 at 5:16
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    \$\begingroup\$ Yes and the levels did not drop. When the battery is not charging or being discharged no activity is created by the plates consequently no water is evaporated or driven off. The batteries are closed so nothing can escape to the atmosphere except via the vent caps. The fact that you have to keep adding water indicates you are probably overcharging them. \$\endgroup\$
    – Gil
    Nov 13, 2022 at 19:37

When battery is in use for some time, some residue appears on the bottom.

To drain the acid you will have to turn the battery upside down, so the conductive residue can short the plates.

  • \$\begingroup\$ nice! I was planning to use a siphon or something on those lines, but this seems to be a truly valid point to consider while draining a used battery. Did you even perform this procedure? And do you know if this works only for new batteries or can be done on used ones too? \$\endgroup\$
    – Anchovy
    Nov 8, 2022 at 10:15
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    \$\begingroup\$ @Anchovy Yes, siphoning the electrolyte out should be safe, but if there's a lot of sludge at the bottom, it might keep blocking your siphon. And for the love of (deity), please don't even think of starting the siphon by sucking with your mouth (yes, sounds ridiculous, but you would be surprised how creative some members of our species are). \$\endgroup\$
    – TooTea
    Nov 8, 2022 at 10:22
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    \$\begingroup\$ @Anchovy Yes, those are pieces of the electrodes which have fallen off. The electrodes are basically lead grids packed with a "paste" containing lead metal/lead oxide/sulphate. As the battery charges and discharges, this paste contracts and expands, so it will gradually break up and fall off. Very old and/or mishandled batteries can lose a significant fraction of electrode material this way (which is how they lose capacity), or a big chunk can get stuck between the electrode plates and short out the cell. \$\endgroup\$
    – TooTea
    Nov 8, 2022 at 10:28
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    \$\begingroup\$ @Anchovy: You can only siphon out the electrolyte down to the top of the plates - there is no way to get to the bottom of the cell to get most of the electrolyte. As mentioned elsewhere, even if you could get all the loose fluid out, the plates and separators would remain moist and the battery would continue to self-discharge and sulfate. \$\endgroup\$ Nov 8, 2022 at 16:23
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    \$\begingroup\$ The last paragraph reads as an instruction on what to do. I think it should be reworded. \$\endgroup\$
    – gre_gor
    Nov 9, 2022 at 4:49

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