I bought some used ones at a very good price, but without instructions. The seller included two thin, filmy plastic inserts that fit inside the grips. He said they were intended to protect the twin batteries, but I found it vexing to position them and seat the grip screws. I tried some YouTube videos, they showed the grips being installed with the inserts. Is that what these things are meant for, to protect the batteries from contacting each other? Will the absence of them degrade battery life?