Decoding the ER Battery Designation

The Critical Role of Diodes in Battery Packs

LiSOCl2 batteries are designated with the prefix ER, followed by a size code, for example the ER14505, which denotes a size similar to an AA battery. An additional suffix is used to categorize the cell's internal structure and performance profile:

When LiSOCl_2 cells are combined in series to create higher-voltage battery packs, diodes are essential for safety and reliability. They prevent a dangerous phenomenon known as reverse polarization.

Since LiSOCl_2 batteries are primary (non-rechargeable), they cannot tolerate the flow of charging current. In a series string, if one cell depletes its charge faster than the others, the remaining stronger cells can drive current backward through the depleted cell, causing reverse polarization. This can lead to rapid degradation, venting, or even rupture of the failed cell.

The addition of a bypass diode across certain cells (or, in some cases, the pack) provides a low-impedance path for the current to flow, bypassing the dead cell and preventing excessive negative voltage development across it.

The requirement for diodes is based on the cell's capacity and the size of the battery pack:

Diode Inclusion Rules (LiTHC Battery Packs)

1. ER Capacity Type (No suffix, Bobbin structure)

Diodes are required for combinations that include ER26500 cells or cells with a higher capacity.

Diodes are required for combinations with 6 or more cells (including $6$) of lower-grade $LiTHC$ cells.

2. ER Power Type (M suffix, Spiral structure)

Diodes are required for combinations involving or more cells.

These specific rules ensure that the battery pack operates safely, maintaining power delivery even if one cell reaches its end-of-life early.