  We obtained B and R-band CCD images for the dwarf elliptical (dE) galaxies
DDO44, UGC4998, KK98_77, DDO71, DDO113, and UGC7356 at the NOT. Using Fourier
analysis technique we measure stellar R-band surface brightness fluctuations
(SBFs) and magnitudes in 29 different fields of the galaxies. Independent tip
of the red giant branch distances for DDO44, KK98_77, DDO71 are used to convert
their set of apparent into absolute SBF magnitudes. The results are combined
with the local (B-R) colours and compared with the (B-R)-\bar{M}_R relation for
mainly old, metal-poor stellar populations as predicted by Worthey's population
synthesis models using Padova isochrones. While the colour dependency of the
theoretical relation is confirmed by the empirical data, we find a systematic
zero point offset between observations and theory in the sense that models are
too faint by 0.13+-0.02 mag. Based on these findings we establish a new
semiempirical calibration of the SBF method as distance indicator for dE
galaxies with an estimated uncertainty of ~10 percent. Taking first advantage
of the improved calibration, we determine SBF distances for the other three
early-type dwarfs. Although found in the M81 group region, previous velocity
measurements suggested UGC4998 is in the background. This picture is confirmed
by our SBF distance of 10.5+-0.9 Mpc. We can further identify DDO113 as a faint
stellar system at the near side of the Canes Venatici I (CVn I) cloud at a
distance of 3.1+-0.3 Mpc. The second CVn I member in our sample, UGC7356, lies
at 6.7+-0.6 Mpc and spatially close to M106. We derive BR surface brightness
profiles and colour gradients for all dwarfs and determine photometric and
Sersic parameters. Finally, we discuss two objects in DDO71 and UGC7356 which
may resemble GCs.
