Eh Greg? He isn’t dumping everything into the battery box. The MV battery box that only has two batteries in it should only be able to take 2 * 256 = 512 EU/t. The HV-MV transformer should always be full and pumping out 4 * 256 EU packets, of which the battery box can only claim 2, maybe 3, leaving at least one for the MV-LV transformer, and it should only need one packet every 3 or 4 ticks.
I wonder if this has to do with the recent change for battery boxes to only exchange power with the batteries once a second. I’ll bet that if you downgrade to the previous version, this setup will work. With the change, I’m betting the battery box’s larger internal capacitor actually allows it to take the full 4 amps for at least a dozen ticks before it fills up and waits to dump into the batteries on the 1 second mark, which starves the LV transformer.