I'm trying to think.... I don't specifically remember any significant dimming on my pocket with my EMS cart. Which backlight are you using? Also the EMS carts have gone through several revisions, maybe they increased power efficiency? My EMS cart is from 2010 or 2009 I think, so it's fairly old.
Either way, the 32k cart should use as little power as possible. The datasheet for the eeprom says it only uses 12mA, so basically nothing. I would be shocked if it caused dimming at all.