Tesla is putting continuous efforts into making its battery packs safer. We saw a great example earlier this year when we reported on Tesla setting fire to a Powerpack to test its safety features with impressive results.

In its latest effort, the company filed a new application for a patent for an apparatus and method for ‘charging batteries safely’.

Last year, a Model S had an issue while charging due to a “short circuit in the distribution box” and it resulted in the car catching fire. Tesla said that they addressed the issue with a software update to its fleet to “provide extra security during charging”.

In order to further reduce the risk of a short circuit having a hazardous impact — though this time at the battery cell level, Tesla developed a new methodology to monitor the cells and detect a short circuit.

Here’s the abstract from the new patent application:

“An apparatus and method for identifying a presence of a short circuit in a battery pack. A fault-detection apparatus for a charging system that rapidly charges a collection of interconnected lithium ion battery cells, the safety system includes a data-acquisition system for receiving a set of data parameters from the collection while the charging system is actively charging the collection; a monitoring system evaluating the set of data parameters to identify a set of anomalous conditions; and a controller comparing the set of anomalous conditions against a set of predetermined profiles indicative of an internal short in one or more cells of the collection, the controller establishing an internal-short state for the collection when the comparing has a predetermined relationship to the set of predetermined profiles.”

Tesla says that internal cell shorts in the industry happen about 1-5 times per million cells, which would translate to one cell every ~30 to ~150 cars assuming ~6,000 cells per car and the same failure rate for Panasonic’s cells – though that’s not necessarily true (updated to better reflect failure rate per million). Even though it’s not a common occurrence and that it wouldn’t necessarily lead to a hazardous situation, the ability to detect an internal short remains useful. That’s what the new method describes.

The battery management system would then be able to identify the single cell that is the problem and Tesla could simply swap the module and repair it.

Several Tesla engineers worked on the new system, including Kurt Kelty, Tesla’s longtime director of battery technology. They filed a new application for the patent only 4 months ago and the application is now being released.

Here it is in full: