A guide to customizing lithium polymer batteries

Last updated March 1, 2023

It will not only affect work efficiency but will also lead to misconceptions about poor performance if the customized lithium polymer battery has incomplete customized information. More importantly, it may cause a greater safety hazard to the product. Therefore, AllrunBattery summarizes its experience in customizing lithium polymer batteries for customers’ reference, it will be very helpful for either project product design or custom battery solutions.

The finished thickness of a lithium polymer battery

Due to the expansibility of the polymer battery itself, all LiPo batteries will expand after charging and discharging a certain number of times, so the thickness expansion rate should be considered when designing the product. If you don’t believe it, you can test the thickness with a lithium polymer battery caliper, at least 6% deviation from the expected thickness.

The width of a lithium polymer battery

In polymer batteries, the edges will loosen when the battery is folded since they generally utilize single-fold or double-fold technology. A folded edge, for example, was 18mm wide at the time of folding. After folding, the folded edge will loosen and the width will become about 18.3mm. It is also time to test product designers, so don’t forget to leave more space for batteries.

The capacity of lithium polymer batteries

Depending on the battery space, the battery capacity range can be accessed up to a certain level, but not up to 100%, so the custom battery manufacturer will indicate the upper and lower limits of the battery capacity. For example, the design capacity given by the evaluation manufacturer is 150mAh, and it will appear 145mAh. It’s normal to have positive and negative tolerances on designs, so don’t bite the word too soon.

The voltage of lithium polymer batteries

There is a difference between high voltage and normal voltage. For example, if you are using a 4.35V (full charge) voltage system, the lithium polymer battery’s instruction manual must clearly state that the normal voltage is 4.2V (when fully charged). Generally, the 4.2V voltage system is customized if you don’t explain it clearly. To determine which voltage system would be suitable for your product, you should first understand the power supply scheme of the chip.

Working current of the battery

Different products have different working currents. For example, the working current of a smartwatch battery is relatively small, and 0.2C discharge can meet the use requirements; while the working current of a model airplane battery is very large, generally around 15A, and a 1500mAh model airplane battery can continue to discharge at 25C. Therefore, when customizing the battery, you must understand the working current, such as how much A when working continuously, and how much A when working instantaneously.

Battery pole ear

Especially when dealing with soft pack batteries, it is important to consider their overall size, as well as the size of their positive electrode, since their positive electrode is remarkably fragile and easily breaks when folded multiple times. When in use, the positive electrode is most often laser-transferred to nickel. Based on experience, the positive ear should not bend more than three times. The problem of easy ear breakage can be solved by using thick and wide lithium polymer batteries customized for the battery capacity.

The output of a lithium polymer battery

A small polymer battery‘s output is mostly wire, and some of it is battery terminal wire, which has different terminal types, including JST terminals, PH terminals, 1.25 terminals, 2.0 terminals, 2.54, 3.96 terminals, etc. Additionally, there are positive and negative terminals. When the connection direction is incorrect, the product will not work, or may even burn out. If you are not sure, you can provide the plug-in socket and battery power input circuit to the other party, or communicate in person to ensure that the battery customization will not go wrong.

Finished battery pack

Finished batteries usually have protection boards, wires, plug wires, and casings. Special batteries, such as those used in Apple mobile phones, may require flexible FPC cables, and some may require plastic shells, such as those used in walkie-talkies. In the process of customizing lithium polymer batteries, items such as high current, shell and shell color, silk screen, communication protocols, etc., must be clarified, such as high current, shell and shell color, silk screen, etc. The more detailed the content, the fewer errors will occur.

Battery surface

Lithium polymer batteries have a very delicate surface, and it is easy to scratch if you are not careful. Do not intentionally scratch the battery surface. During incoming inspection, customers should not scratch the battery surface. These unnoticed behaviors need to be stopped. We encourage you to support the customization of lithium polymer batteries by various manufacturers, to communicate more, to tolerate more, and to cooperate more.