The Obstacle Course on the Path to Repurposing Used Electric Vehicle Batteries (EVB). Part III: Lack of Critical Battery Information

This is the third blog in our series, this time we’re going to discuss the (lack of) access to critical information needed to repurpose EV batteries. Batteries are complex, potentially dangerous systems, and should be designed with safety in mind. Unfortunately, used batteries often don’t come with a manual or datasheet. Believe us. Since 2018, we have tested over many different battery types, four of them were used and from third-party sources. This presents a few challenges when it comes to testing and also repurposing the battery.

In this blog, we’ll discuss:

• Low hanging fruit: battery details that are readily available

• data you need to gather yourself, and 

• information that is nearly impossible to get (but may be critical for repurposing).  

  • This includes some public comments we sent to the California Air Resources Board (CARB) in response to their latest regulatory proposal on Advanced Clean Cars II.

Low hanging fruit: battery details that are readily available

Basic battery specifications: For starters, you’ll need to know whether the battery is a cell, module, or pack configuration. Then there are the key metrics like nominal ratings for voltage, capacity, current, and temperature.  You’ll also need mechanical parameters such as dimensions, shape, and mass. This information tells you what your battery building block is. 

Depending on the battery of interest, you may be able to find this information online, or you may have to do some quick series/parallel napkin calculations to make educated guesses. If you already have the battery, check for labels or nameplates that may display rated electrical and mechanical parameters. In any case, if you don’t know these basics, it’ll be extremely difficult to even design a second-life battery system.

Material safety data sheet (MSDS): If you know the part number, you may be able to find this with a quick Google search. This MSDS is required to ship a lithium battery since it is considered a hazardous material.   Note: this is still not available for Tesla batteries, even when an owner requests it. 

Data you need to gather yourself

Knowing historical usage patterns and environmental conditions helps understand how a battery may have degraded over its life. This is important to know for state-of-health (SOH) as well as safety assessment. Some of these key metrics include but are not limited to:

• historical average (state-of-charge) SOC: 

• peak charge and discharge currents, 

• average charge and discharge currents, 

• number fast charge events

• Average peak charge voltage

• average temperature

• Past fault codes

• Odometer readings

But where do you find this information? For most of it, you will need access to the battery management system (BMS) and software that can read the BMS. This is a big obstacle. In our experience sourcing used batteries, automakers often remove the BMS as there are components of this that are deemed proprietary. Furthermore, the software that can read the BMS data is not available on the open market.  In rare cases where it looks like it is, the license may be for batteries only available in a different country. 

State-of-Health Assessment

For many EVs, SOH information is not always known or made easily readable, but that may change soon (see CARB section below). Without this information, capacity testing needs to be performed, normally through battery cycling. We won’t go into detail here, but you can read about that in Part II of our Used EV Battery blog series here. You can also read about building your own battery cycling equipment in our two-part blog here and here. 

Advanced Clean Cars policy from CARB 

The California Air Resources Board (CARB) is working on Advanced Clean Cars II policy recommendations to reduce GHG from new light- and medium-duty vehicles beyond 2025. In a recent workshop, CARB presented on draft battery durability requirements that require 10 year/150k mile battery warranties, and require OEMs to calculate battery SOH within 5% and to make that readable to the driver without a tool. If executed correctly, this would remove some barriers to repurposing passenger and medium-duty EV batteries. 

ReJoule’s recommendations 

Disassembly/removal instructions: This is important for safety reasons, but also to encourage that components are not damaged by improper removal. This encourages that more subsystems can be repurposed, and the cost of repurposing can come down (Battery pack, BMS, cabling, fuses, DC contactors). For more on the challenges of disassembly, check out our blog on our own challenges on disassembly.

Prior Safety Certifications: Having battery test summaries from EV safety certifications can reduce safety testing costs for second-life batteries. For example, durability testing for automotive (shock, vibration, overcharge, thermal runaway, etc) are similar to safety testing for stationary storage, but the standards require that battery packs be re-tested. Re-testing makes certification extremely expensive.

Reuse as much as possible: 

The historical data from the BMS should be accessible to 3rd party testers, and fault messaging and monitoring should be made available over the CAN bus. To take it a step further, as much of the original BMS, including monitoring hardware, DC contactors, fuses, cabling, busbars, and mechanical enclosures should be reused. This can significantly lower second-life battery engineering and system costs. If a repurposed battery requires a new BMS for each battery pack, the cost savings from used batteries are diminished.  

What are your thoughts? Did we leave anything out? Please comment and share so we can all engage in conversation and learn from each other.  Contact us at info@rejouleenergy.com if you want to leverage our technology to test your batteries.

Cheers, 

The ReJouligans

Legal notice:

This document was prepared as a result of work sponsored by the California Energy Commission. It does not necessarily represent the views of the Energy Commission, its employees, or the State of California. Neither the Commission, the State of California, nor the Commission’s employees, contractors, or subcontractors makes any warranty, express or implied, or assumes any legal liability for the information in this document; nor does any party represent that the use of this information will not infringe upon privately owned rights. This document has not been approved or disapproved by the Commission, nor has the Commission passed upon the accuracy of the information in this document.©2021 ReJoule Incorporated.  All Rights Reserved.

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