Shortening them will consume proportionally less power and thus increase the battery life. It may not make them much brighter, it depends on the inverter and how “taxed” it is driving the length. Since inverters generally don’t allow you a choice of voltage (it’s > 100 VRMS) it is what it is. Could you run a nominally 12 V inverter on less voltage, say 2 LiPos in series (~7.4 V), and have that work with a shorter lengths ? Good question, I don’t know. It would depend on the inverter design and I would guess there’s some min voltage input for it to work at all. E-mail SFE tech support with that question.
ps - one other thing to be aware of … some inverters do not like being disconnected from a load. They depend on some min length of EL wire being attached or else bad things happen. SF says theirs all operate w/o any load.
pps - It occurs to me that maybe, just maybe, if really needed, the EL Sequencer board could be modified to allow 2 inverters to be attached and to split/divide their outputs to go into different output channels. For instance channels A, B, C, and D could run off one inverter and E, F, G and H the other inverter. I’ll have to look at the board design and see if there’s a place where an easy cut w/an Exacto knife will do the trick.