# What are the tradeoffs when building a modular battery pack

I want to build a 120 v / 128 Ah battery for an EV conversion project (small car with short range). I plan to base this on 18650 size lithium-ion batteries (recovered from old laptop battery packs).

To enable distributing the batteries around the car, I would like to do this with a number of modules wired together.

My first idea was to have 34 modules (34 x 3.6 = 122.4 v) of 64 cells (assuming ~2Ah capacity, so 128 / 2 = 64) wired in series.

I could also do this differently with fewer modules of higher voltage.

What are the considerations here and what are the benefits/drawbacks of choosing modules of different voltage/capacity? If the modules are spread around the vehicle, would my initial idea of 34 modules in 64p configuration lead to more resistive losses?

• Matching cells in series strings is just as important as parallel cells if using the max C rate charge/discharge values. This is the key part I am interested in as I would like to use the full C rating of the cells. Would you be able to elaborate on that? – Matthew Dresser Sep 5 '18 at 9:00