All production EVs that I'm aware of use a modular battery: Enertia uses 6 Valence U1-12XP modules; 2012 Zeros use 1-3 ZF3 modules; Enertia Plus uses 2 BPM 44/70 modules; Empulse uses 7 BPM 15/90 modules. Making it modular makes it easier to diagnose and repair when faults crop up.
What we haven't seen much of are modular systems which allow varying capacity batteries to be constructed. MotoCzysz's 2010 E1PC went with this approach. One interesting wrinkle here is that the above e-motos connect the modules in series, where for a variable capacity approach you want to connect the modules in parallel (to keep the system voltage fixed). I assume the Exovolt system connects its modules in parallel.
Here's one builder who's making a variable-capacity removable pack for his e-moto:
http://www.elmoto.net/showthread.php?2439-The-Battery-Module-Project
