The ModelGauge m5 EZ option is good for most applications that use the most common lithium chemistries: LiCoO2 (most common), NCA/NRA, and LiFePO4.
For other chemistries and for the highest level of accuracy, a custom battery model is needed. Maxim provides a battery characterization service for projects with at leask 10k volume, which you can initiate by contacting your FAE or Technical Support. Because the characterization process relies on accurate knowledge of the system load profile, it is best to wait until the end of your project's design phase to start the characterization process. Use the EZ model during the development phase of your project. The process involves getting detailed system information, along with 3 or 4 battery packs for Maxim to characterize. Once we receive the batteries, the model is typically ready in 2-3 weeks, so plan to start the process about 4-5 weeks before the model is needed.