The old Wixey gauges used button batteries which had a limited life. As the battery neared the end, the readout would start varying -0.1 to 0.2 degrees. The newer models use AAA batteries which have a much longer life.
It is important to understand, even though the display may be off (manually or automatic) the circuitry is still operating to maintain calibration and still drawing on the battery. With a good set of batteries you can expect most newer models to run much longer- angle cube WR300 and WR300BT(w/Bluetooth), tilt and level gauge WR365, planer thickness gauge WR510, remote planer thickness gauge WR550, etc. Battery life for the Bluetooth and back-lit models may be less.
The operation of any of the planer or router table gauges depends on the installation- install it wrong and it won't work correctly. Everything must slide smoothly and freely. It it doesn't you will get bad readings. I have Wixeys on my RC51 20" planer (and on a DC380 15" planer before that), table saw fence and tilt readout- I added an arm with small bracket to the height wheel and am able read blade tilt continuously without moving the tilt gauge to the blade. I have been using them for years. I have another unit, but never got around to installing it on my router table because the height of the bit can change, depending on how it is mounted in the collet. I find it easier to use a height gauge on the bit itself. I never got one for my dual drum sander but I could use it on my current projects.
Bottom line, the current set of Wixey gauges are reliable and have longer battery life.
Original, vertical display, Wixey thickness gauge on my 15" planer:
I put a newer angled display (easier to read) unit on my 20" planer before switching that one to a remote readout Wixey unit. (No pic but the remote readout is mounted to the infeed side and the measuring unit and mechanism is mounted at the outfeed side)
With my mitersaw installation I can't see the tilt scale which is at the back of the saw so, using an existing cable clamp screw at the top of the saw, I added a small steel bracket where I can set the Wixey. Setting the tilt must be done when the saw head is fully down as shown in the pics. (I did this after forgetting to take the Wixey off the blade before turning on the saw- flying Wixey!
I added an arm and small steel bracket to the elevation wheel on my table saw. At the start of a shop session, I use the Wixey to set the blade to 90° to the table (vertical). Then I relocate the Wixey to the bracket and calibrate it to 0°. After that it tracks and precisely displays table tilt (saw does not need to be level. If you look at the display, you'll see the absolute level is 15.4° which is the tilt of the mounting bracket.
I don't use the Wixey on my tablesaw often, but it is great for indexing in the "incremental" mode.