As above, A good bit of kit. I use it via the power cable, on the C150/172 I fly, so cannot comment on battery life. However, mine will not start up on the cable with flat batteries, so you always need a good set of cells in it plus a spare set.
I use the Bean bag mount which is quick, easy and appears to be stable. Like others I only update mine once a year after I have got my new chart. I use it as an addition to chart and compass and a prepared log.