Simulate in SPICE, sure -- I wonder actually if you could use a PN diode with a preposterously large transit time, the physics is very similar; but more likely, you're going to want to be able to set the state of charge, and so you'll need a dependent capacitor. In series with that, some RCs to model ionic diffusion (as applicable; this is responsible for voltage recovery on discharge, and for current tailing off during a float/finishing charge, as used with lead-acid and lithium-ion types).
IRL -- can't really imagine it's worth it, compared to a real battery. An electronic load of adequate size is going to be pretty pricey. If you just want to test load capacity, yeah, a bunch of heaters would be something.
Tim