I've just replied to your second question, not having seen that you want to bring the hedge down to a reasonable height!
You need to be able to buy this in person so that you can try a couple out for weight and balance. Bear in mind that the battery packs can be very heavy. Is a corded trimmer out of the question due to distance from electric socket?

Also, you need to consider that a hedge trimmer may not be powerful enough to cut through the stems at the lower level. I cut down my 10 ft high 100 year old privet hedge using a combination of long handled (string pull) lopper and bow saw for the very thick stuff.
I struggled with the bow saw and went to the garden centre to buy something better and got the lopper - best bit of garden kit I've ever bought - got the biggest part of the job done in a couple of hours.

PS - it's actually a "telescopic bypass tree pruner" and it has a cut up to 32mm diameter. The beauty of it is that very little effort is needed to pull the cord to make the cut.