Sumaru's plan with the capacitor units is not to charge his weapons or it's normal use in powering up his teleportation pack. Instead, his plan is to use it as a backup power supply to his suit, in the case that he enters one of these superior anti-aether fields. Seeing how the Mindy is powered by a aether generator, it would simply shutdown without a secondary source of power for life support and other integral systems such as the AIES. That's where the capacitor units come in, if they provide enough power that is.