Depends… You need to report the diagnostic trouble code (DTC) that is causing the IMA light to illuminate so that we can better understand the condition of your battery pack.
I think most people feel that once the IMA light illuminates, balance-charging with a grid charger would likely not restore the battery pack completely because too much degradation and possibly irreversible damage has already occurred. But balance-charging would almost certainly improve the battery pack's performance and extend its life significantly, so it's worth buying or building a grid charger because you could use it to maintain a future new battery pack.
Uppsala, Sweden: 2000 Insight A/C #559 with Honda security system, Genesis One MIMA+FAS and grid charger, OBDIIC&C, Rostra, Fumoto, DEFA engine block heater, Philips LED DRL's
Honolulu: 2012 Mitsubishi i-MiEV