This breakout session is a brief overview of how to do cell binning and building a balance battery pack.

Balancing

Implementing active balancing is challenging and requires a dedicated team member
Passive balancing will waste precious energy. Pack-level balancing (i.e. force the voltage of all modules to be the same) can be done by connecting all modules in parallel. However, if there is a damaged cell, it will consume all the energy and heat up very quickly
Building well-balanced is more effective

Battery approval

It is necessary to acquire detailed technical documents from the manufacturers
It is encouraged to submit battery approval form early and revise it based on Steve’s comments

Fresh battery cells might be in a particular state as specified by the manufacturer
A new cell be in discharging or charging part of the hysteresis loop
A new cell might has some energy (usually nominal voltage) in it but it’s unlikely to be 0% or 100%

Cells might varies in impedance, capacity, weight, number of cycles, and physical dimensions
The impedance and capacity of a batch of cells should follow a normal distribution. An non-normal distribution is an indication that the cells are not in the same manufacturing lot or pre-binned in the factory
Ordering cells in the same manufacturing lot may reduce the variation
Some manufacturers offer low-grade (i.e. low capacity) battery at a discounted rate. These cells are binned at the factory (separated from the high grade cells). They might have lower variations, which might perform better than a better but mismatched batter pack

Prepare a set of good quality backup modules
- Ideally we should have enough modules to build another pack
- Recommended to buy 3 times of the number of cells in a pack
Cycle the backup modules to match the operating modules to have the same characteristics

The voltage loss due to the bus bars and wires between the modules might be significant under high current
Use Kelvin sensing to mitigate the issue?

Measurement equipment should be 10 times better than the variations
Compare the battery module's actual performance with the predicted performance
Be careful of over-stressing the cells if the current load is too high (use step voltage/current)

Consider mechanical vibration and stress
Anderson connectors' mechanical bonding between the contact and the housing might breakdown early than expected
Prevent short circuit due to foreign objects or human errors