Upgrading the battery - Tesla pack

Post date: Nov 1, 2018 2:16:01 PM

In the Mazda, we have a total of 64 prismatic 100Ah cells from Winston. It is divided into 2 packs at ~100V and is good for about 20kWh. Unfortunately, the energy/weight ratio of LiFePO4 cells is not very good compared to other Lithium chemistries. This makes the car feel quite heavy and close to its maximum allowed weight. However, at the time, these cells were affordable, obtainable and not too difficult to work with.

But we always dreamed of building a pack from better cells with a higher energy content. Common cylindrical 18650 cells are interesting and can be welded together with a spot welder and nickel strips, just like an e-bike battery. Still, sourcing such a cells, testing and assembling them is not a straightforward task.

In the summer of 2018 we started to discuss the possibility of using modules from the Tesla Model S. Several sellers offer the 25V 5.3kWh modules at prices around 1200-1300 Euro, which makes them somewhat more expensive than assembling your own pack from individual 18650 cells.

Looking for crashed Teslas, however, shows that it is possible to buy a complete pack from a car with reasonable mileage. The unused modules we could sell again...

Since we want to keep the existing drivetrain, we are constrained by the voltage range of the the controller and charger, which is around 130V. So, we can put 5 modules in the car for about 25kWh, or 10 if we again use 2 packs. But in the latter case, the weight would be even higher... Or we need to switch to a higher voltage drivetrain... but then the upgrade becomes a complete rebuild...

Several car breakers were contacted and eventuelly we bought a pack from a Tesla P85D in the Netherlands, and got it transported.

Opening the pack involves a lot of work. Everything is glued, screwed and overall very stuck. We worked around with a hammer and chisel until the top cover came free.