One of the most frequent charging questions we get is from LFP Tesla owners who are curious about why our charging guidance seems to conflict with Tesla’s charging guidance.

While Recurrent recommends trying to keep all batteries between 30% and 80% state of charge, Tesla tells LFP drivers it’s OK to charge to 100% for daily drives, and recommends doing so at least once a week.

Why the discrepancy? Two things:

  1. LFP chemistries are known to hold up better to high charges than NCA or NMC batteries. This means that an LFP battery charged regularly to 100% will, over time, degrade less than a different battery treated the same way. Since LFP batteries have lower energy density, the extra bit of charge means an equivalent range for cars with these packs. However, for all lithium ion batteries, avoiding a full charge will prolong life. It’s just that it may not be as noticeable a change with LFP packs.
  2. Tesla’s battery management system (BMS) will be more accurate if it can recalibrate at 100% state of charge. This is true for all Teslas, but particularly true for LFP models. Why? LFP batteries have a very flat voltage curve, which means that it’s harder for them to calibrate at 80% than it is to calibrate an NCA battery at 80%. Read on to understand more about this.
The charging guidance on an NCA based Tesla

Nerdy aside: Why a flat voltage curve makes the BMS job’s harder

With NCA batteries, the voltage increases pretty linearly as the state of charge increases, and decreases as the state of charge decreases. That means the BMS can use voltage information, which is relatively easy to check, to estimate the state of charge. However, in an LFP battery, the voltage does not vary as much with state of charge. This makes it harder to use voltage as a predictor, especially when it comes to individual cells. By charging to 100% periodically, the BMS has a “set point” to recalibrate its capacity prediction, and hence the accuracy of its range estimates.

Curious to dive deeper into how the BMS works, and why charging to 100% may help calibrate?

Or, do you want to learn more about LFP battery chemistry?