Hozelock AC Plus timer battery glitch?

My Hozelock AC Plus timer stops working when screws to the battery compartment are too tight. Even when the screws are loosened, the power from the batteries is sometimes lost. This same problem occurs on 3 different units so seems to be a design flaw. Has anyone had the same problem, and found a way to fix this? The terminals look fine and the batteries are new. Removing the cover and fiddling with the batteries does reproduce the problem, but it does not appear that there is a glitch between the terminals and the batteries (eg inserting baking foil does not solve the issue) - so I am a little mystified as to what the problem is.