it could be dampness in the collars,try drying them out and then wrap insulating tape
around them and test again,also new batteries don't mean a thing to me as they are draining/leaking all the time,whenever you buy a new set of batteries test them with a multimeter for voltage readings,
Higgins
Recently went out with a lad off here, i had my MK1 he had a mk3m, cold horrible day, he had readings of 6+, i showed readings of 3ish.
So, in conclusion, I don't have a clue