Why Can't Lithium Thionyl Chloride Batteries Be Connected in Parallel Axially?

Lithium thionyl chloride (Li/SOCl2) batteries cannot be axially connected in parallel due to several reasons:

1. **Internal Resistance Variations**: 

Each cell may have slight differences in internal resistance. When connected in parallel, cells with lower resistance may dominate the current flow, leading to uneven distribution and potential overheating or failure of those cells.

2. **Voltage Mismatches**: 

If the cells have slight differences in voltage, this can cause excessive current flow between the cells, leading to one cell discharging into another, which can cause damage.

3. **Thermal Runaway Risk**: 

In the case of any imbalance or failure in one cell, the heat generated can cause thermal runaway, which is dangerous and can lead to leakage or explosion.

4. **Chemical Stability**: 

The chemistry involved in Li/SOCl2 batteries is sensitive. Parallel configurations may exacerbate issues related to gas generation and pressure buildup.

For these reasons, it's generally recommended to connect Li/SOCl2 cells in series for applications requiring higher voltage, rather than in parallel.