Gotcha - thanks16.8v if you *really* must, but do not go higher than that.. Battery packs (especially new ones) can be quite a bit higher than the 'published' figure when new.
Wouldn't want to do it any harm. The first one is going well in the blue and yellow dismal which, interestingly, is a metal body (nickel silver Worsley Works etched body).
I took a tip from someone else who said that they put the Rx in the corner of a metal cab - presumably the windows may help a bit - and it's fine