Primary, Ion, and Polymer: a lithium battery primer


Energizer ultimate lithium cells are designed to be a lighter, longer-life direct replacement for the AA alkaline battery.

Lithium primary, lithium ion, lithium polymer…want to know the differences between–and varied uses for–these diverse types of lithium batteries? You’re not alone…so did I.

Recently, a reader asked about the suitability of using AA Lithium batteries in a Tecsun radio.  Several knowledgeable Post contributors–including Richard Langley, Ken Hansen, DL4NO, Eric Cottrell, and Mark Piaskiewicz–responded, and a discussion of the differences in various lithium cells and their chemistry followed.

I was quite intrigued by this discussion, and wanted to learn more; a bit of research ensued. The wonderful folks at came to my aid, clarifying the compositions of these various batteries and enlightening me regarding their unique applications.

Following is a (nutshell) primer describing what I’ve recently gleaned from these experts on the subject of lithium batteries. First, a brief disclaimer: the scope of this article is modest, explaining briefly the roles and compositions of the most common lithium batteries used by consumers and hobbyists/enthusiasts. So, if you’d like an even more detailed discussion of batteries, please check out the Battery University website.

With that said, there are generally three types of lithium cells:

1. Primary Lithium (non-rechargeable)

Though this SAFT battery looks like a typical AA, it produces a whopping 3.6V and will certainly fry a radio that is expecting 1.5 volts from each AA cell.

Though this SAFT battery looks like a typical 1.5 V AA, it produces 3.6V and will fry most radios.

Primary Lithium batteries are single-use and should not be recharged under any circumstances. These batteries have a high charge density (i.e., a long life), and as a result, cost more per unit than other single-use (disposable) batteries, such as alkalines.

Primary lithium cells generally produce 3.6 to 3.7 volts; however, there are manufacturers (Energizer and Duracell, to name two) who have developed cell chemistry that lowers this voltage down to 1.5 volts per cell, thus creating a safe, direct replacement for the common AA alkaline battery.

Unless you are purchasing a battery with a AA form factor from Energizer or Duracell, you should double check the voltage of the battery you are purchasing. There are many manufacturers who produce a 3.6 volt primary lithium batteries that have the same dimensions, or form factor, of an AA battery (see photo right), but are used in specialty medical, military, industrial and testing applications in which voltage requirements are higher.  These cannot be used interchangeably with conventional AAs, as they will cause harm to a device.

In other words, do your research when purchasing a primary lithium cell! Make sure the voltage matches what your electronic device requires–or as Post contributor, Richard Langley, puts it–“Caveat emptor!” (Buyer, beware!)

2. Lithium Ion (rechargeable)

Lithium Ion packLithium Ion batteries are currently one of the most popular rechargeable batteries for consumer electronics on the battery market. There are a number of Lithium Ion variations with their own unique chemistries–and their own unique characteristics–but in general these have a high energy density, a modest memory effect, and exhibit only a gradual loss of charge when not in use.

Generally speaking, Li-ion batteries are not available in voltages most radios and other electronics would need, from, say, AA, AAA, C, D, and 9V alkaline. There are manufacturers who produce Li-ion varieties in a AA form factor (they look like AAs), but which produce more than double (3.6V) the peak voltage of an alkaline AA (1.5V); thus, these lithium batteries, too, can only be used in devices designed around these higher voltages–such as specialty flashlights, military, industrial, and medical equipment.

There are a number of radio manufacturers using slim Li-ion battery packs like the one in the image above.

3. Lithium Polymer (rechargeable)

Most LiPo batteries come in a "pouch" format, designed for specific applications,

Most LiPo batteries come in a “pouch” format, designed for specific applications,

Lithium Polymer (LiPo, LIP, Li-poly) are rechargeable battery packs that generally produce 3.6 – 3.8 volts when charged. LiPo packs have much of the same charge and  discharge characteristics of Li-ion batteries, however, they are lighter in weight and can be designed to fit almost any shape.

LiPo batteries have a very strong following in the world of radio-controlled aircraft and cars–their feather-light weight as well as gradual discharge curve render LiPos almost ideal for these applications. LiPo packs are also used in consumer electronic, solar, and GPS applications, to name a few. LiPo pack variations are currently being considered for use in electric and hybrid vehicles.


And so, returning to our original post questioning the use of Lithium cells in reader Philip Dickinson’s Tecsun PL-606, the Tecsun representative was absolutely correct:  these batteries, it turns out, are not suited for this application, as the voltage is too high for safe use in this Tecsun.

Since I didn’t have a link to the batteries Philip purchased, I assumed Philip might be referring to Energizer Ultimate Lithium AA batteries, which are direct 1.5V  replacements for alkaline AA batteries (and why I use an Energizer graphic in the post).

At any rate, it appears that Philip purchased 3.6V primary lithium cells in a AA cylindrical form factor. If he does pop these AA lithiums in his PL-606, it will surely fry the radio as the voltage is more than double what this radio actually requires.

Hopefully, Philip can return these lithium cells and replace them with the Energizer or Duracell 1.5 V AA variety.

Philip, thanks for writing in with this question; learning about lithiums has been most interesting!  And hopefully, this primer you’ve invoked will save other radios from harm: readers, do check your voltage requirements before you insert those lithiums.

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13 thoughts on “Primary, Ion, and Polymer: a lithium battery primer

  1. Paul S. in CT

    Actually according to wikipedia, there is another Li-Ion type Li-Fe-PO4 (Lithium Iron Phosphate. It is this chemistry that is used in electric vehicles due to having a much lesser fire-hazard risk. The Voltage is 3.2 operating and 3.6 recharge. They make ideal use for multi-alkaline (2 or 4 cell) devices using a dummy cell in series. Most of what is used by the Consumer is the Lithium Cobalt formula, that has a fire-hazard risk. The drawback is that a Li-Fe-PO4 AA cell is usually rated 600-700 mahr: primary cells are 2500-3000 mahr. IIRC Li-Co types are usually around 1000 mahr.

    Paul S. in CT

  2. Eric Cottrell


    The internal battery in my CommRadio CR-1 is a 18650. I noticed some home improvement stores carrying 3.7 volt lithium rechargable batteries in various form factors as replacement batteries for solar lights and other outdoor solar charged devices.

  3. Ayar HB9EVW

    You are absolutely right! What I meant is that the form of the 18650 batteries is similar to AA batteries (cylindrical) and not flat or square etc. They are bigger of course! Sorry for the confusion.

  4. Ayar HB9EVW

    Just a small remark: Li-Ion batteries with AA form factor (like the Panasonic 18650) are also used in full electric vehicles like the Tesla Model S and Mercedes B-Class Electric.

    1. rcxb

      18650 batteries (as used in laptop battery packs and electric cars) aren’t a AA form-factor… They’re too big, and closer to C battery dimensions. (those plastic carriers in LED flashlights that hold 3xAAAs side-by-side are that same size, which is why those are so common) It’s really 14500 Li-Ion batteries that closely match AAs.

      The first two digits are diameter in mm (so 14mm wide). The other 3 digits are the length TIMES TEN in mm (so 50.0mm long).

    2. Mark Piaskiewicz

      I’ve heard that Teslas use 18650s before and I have to admit to being somewhat skeptical about this. It would make far more sense if these vehicles used custom sized cells with a square (or rectangular) shape just for greater energy density per unit of volume. Using round shaped cells would seem an unnecessary waste of space.

      1. rcxb

        You can’t just pack a bunch of batteries together like that. They get hot when being quickly drained and VERY HOT when fast-charged. The natural air-space around round cells could actually be a huge plus for Tesla…

        18650s have the advantages of being available off-the-shelf, and a huge market demand and multiple competitors producing them, keeps economies of scale up, and competitive pressures high. Compared with the cost, which dominates, a little bit of extra volume (and it is only a little bit, as cells can easily be staggered) hardly matters.

        “The small cell size enables efficient heat transfer, allows for precise charge management, improves reliability, and extends battery pack life. Each cell is enclosed in a steel case which effectively transfers heat away from the cell. The small size makes the cell essentially isothermal, and its large surface area allows it to shed heat to the ambient environment.”

    3. Joe In Orlando

      Nothey are NOT A 56mm form configured as 18650 is what vehicles and aerospace applications use as a CELL to MAKE their batteries It isa 3.7v 3-5 amp Lithium or Lithium Iron Pgosphate cell. The forner is inflamableelecrtolyte, the latter isn;t


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