Don't equip any food converter before you get a structure grade converter. It seems like a bug where the converter don't work if you equip the converter you get from Nola or the trader first. I haven't tried to equip any other converter you can find/buy which are not structure but when I equip a structure grade converter as my first converter it works.Cheers, that looks like it worked.
Nevermind, after about 15 minutes the problem has reappeared. taking off all the cyberware, staying fully fed, and with the conversion rate now at 65% still lets my battery drain.