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Size design guidelines for battery chambers and
terminals in battery-operated equipment

Introduction

The Battery Association of Japan (BAJ) has issued the "Safe Design Guidebook for Battery Chamber and Terminals in Battery-operated Equipment" with the aim of preventing accidents involving batteries, and it is requesting that all designers of battery-operated equipment pay heed to safety in their designs. This has led to an increase in equipment that incorporates designs to prevent issues such as reverse battery insertion and short circuits. However, in some devices, problems have occurred as a result of device battery terminal designs that have not fully taken JIS-specified battery terminal sizes into consideration.

In light of this, the BAJ has posted these guidelines on its website, available free of charge. In order to increase customer understanding, the guidelines include "Size Design Guidelines for Battery Chambers and Terminals in Battery-operated Equipment," which focuses on items that we consider important, in particular size design of battery chambers and terminals. These guidelines have been prepared with the understanding that battery-operated equipment will be used not only in Japan but also overseas. Thus, we have tried to ensure that batteries can be used in as many countries as possible by stressing consistency with international regulations regarding batteries (IEC standards) and JIS. Accordingly, these also provide representations of desired configurations. However, diagrams included in these guidelines are only examples, and ultimately requests, but we hope that these will be useful in preventing mismatches between batteries and devices resulting from issues concerning dimensions and configurations.

When considering using devices with battery sizes and configurations not detailed in these guidelines, please consult with battery manufacturers or distributors. Additionally, when designing equipment based upon these guidelines, if there are any unclear points in regard to details, or if further explanations are necessary, we recommend that you directly contact battery manufacturers or distributors.


Batteries covered

These guidelines cover cylindrical zinc-carbon, alkaline manganese, and nickel-based batteries, specifically D, C, AA, AAA, and N type zinc-carbon and alkaline manganese batteries, and AA and AAA type nickel-based batteries.

Designing of the positive contact of an appliance


Figure 1 – Example of the design of a positive contact of an appliance

Figure 1 shows a recommended configuration for equipment positive terminals in order to prevent contact between equipment negative terminals and battery positive terminals, in the event of reverse battery insertion. Equipment positive terminal sizes have been theoretically calculated from these configurations and from battery terminal sizes, and these are summarized in Table 1. Accordingly, in actual design, it is necessary to decide K and H sizes in consideration of tolerance (battery clearance, ease of insertion and removal) between the battery chamber and the battery.

C: External diameter of the contact surface of the negative battery terminal
F: Diameter of the projection of the positive battery terminal
G: Distance between projected surface and second highest part of the positive battery terminal
K: Diameter of the recessed hole as a positive contact with the positive battery terminal
H: Depth of the recessed hole as a positive contact with the positive battery terminal

Units mm

Table 1 Dimensions of battery terminals and recommended dimensions of the positive contact of an appliance in Figure 1

Units mm
Relevant dry batteries Dimensions of the battery terminal Recommended dimensions of the positive contact of an appliance in the Fig.
Negative terminal Positive terminal
Common name Zinc-carbon Alkaline manganese Nickel-based C (min.) F G (min.) K a) H b)
D-type battery R20 LR20 - 18.0 7.8 - 9.5 1.5 9.6 - 11.0 0.5 - 1.4
C-type battery R14 LR14 - 13.0 5.5 - 7.5 1.5 7.6 - 9.0 0.5 - 1.4
AA-type battery R6 LR6 ZR6 7.0 4.2 - 5.5 1.0 5.6 - 6.8 0.4 - 0.9
AAA-type battery R03 LR03 ZR03 4.3 2.0 - 3.8 0.8 3.9 - 4.2 0.4 - 0.7
N-type battery R1 LR1 - 5.0 2.0 - 4.0 0.5 4.1 - 4.9 0.1 - 0.4
Notes: Refer to JIS C 8514, JIS C 8515, IEC 60086-2, and IEC 60086-5
Note a): K should be bigger than F but smaller than C.
Note b): H should be smaller than G.

Designing of the negative contact of an appliance

Some batteries have recessed negative terminal. JIS and IEC specify the maximum recess of the negative battery terminal from the external jacket. (Refer to Table 2) Accordingly, as with the design of positive terminals, the configurations and sizes of equipment negative terminals also needs to be fully taken into consideration, when designing equipment negative terminals.

・ When a spring coil is used as the negative contact of an appliance.

Bend the tip of the spiral spring terminal towards the middle of the spiral in order to avoid damage to the battery label. Ensure that the diameter of the coiled terminal end is smaller than C, the size of the battery negative terminal contact area. A contact pressure that can sustain a good electrical connection is desirable, but an excessive contact pressure can make battery insertion and removal difficult, and can lead to damage to the battery label, and deformation of the contacts.

・ When a flat material plate is used as the negative contact of an appliance

Leaf springs are to be narrower than size C, and in consideration of the maximum indentation E in the battery label, it is necessary to provide a pip (a small protrusion) in order to achieve a reliable connection with the battery. Please avoid a flat connection.


Figure 2 – Example of equipment negative terminal configuration

Table 2 Dimensions of the negative battery terminal

Common name Maximum recessed dimensions of negative battery terminal (max.)
E
External diameter of the contact surface of negative battery terminal (min.)
C
D cell 1.0 18.0
C cell 0.9 13.0
AA cell 0.5 7.0
AAA cell 0.5 4.3
N cell 0.2 5.0
Notes: Refer to JIS C 8514, JIS C 8515, IEC 60086-2, and IEC 60086-5

Important points on designing equipment terminals

In order to extract electrical energy from batteries, it is necessary for there to be a reliable connection between the battery and the equipment terminal. However, equipment configurations and sizes designed to prevent reverse insertion can, on occasion, result in poor contact with the battery. It is also necessary to avoid excessive contact force; therefore we have provided some important tips on the design of terminals.

  • Designing battery chamber configurations and their sizes should not be based upon tolerances using the sizes of batteries from specific battery manufacturers. In order to ensure a reliable connection even when using batteries with sizes at the limits of tolerances as specified in JIS C 8515 and IEC 60086-2, please give full consideration to the design of positive and negative configurations and sizes, and their tolerance.
  • In equipment negative terminals, spiral spring terminals are often used to provide a spring effect at the insertion and removal of batteries, and to maintain contact pressure when the battery is in place. Accordingly, if a spiral spring similar to that used for the positive terminal in the equipment is also used in the negative terminal, then this may result in confusing one for the other, and batteries being inserted with the positive and negative terminals reversed; therefore avoid usage of spiral spring terminals in equipment positive terminals.
  • Equipment terminal contact pressure values for D and C batteries are best from 9.8 N (1 kgf) or more to 29.4 N (3 kgf) or less, and for AA, AAA, and N batteries, 4.9 N (0.5 kgf) or more to ≤9.8 N (1 kgf) or less.

Important points on the design of battery chambers

Having too wide a gap between the wall of the battery chamber and the battery can lead to the battery being mounted within the battery chamber at an angle resulting in poor contact; therefore ensure there is no clearance around the battery.