Montana 700i inaccurate

We have 8 of these units.

Out of box software imported routes to the correct offset measurement 

The updated ones don't route to the correct off course route measurement

Some units switch off randomly and screen does weird stuff though it is actually on.

( is the lithium battery the issue ?

The big one If you create a waypoint in 5m zoom off a shape file and walk back to the way to the way point the way point is up to 10m off.

Come back again off 5m in a different direction.

Brand new out of the box the way point id different again

New or updated to 15.10 its the same. Not good when marking out an area.