Try this, Matt:

A. If the cover is rectangular or square and runs to the edge of the device

1. Press hard on the inside edge of the battery cover. This should be the edge furthest away from where it slides off the main body.

2. Holding the pressure, slide towards the edge.

3. To refit, study the edge of the battery compartment and the underside of the cover. Match them them and apply pressure, then slide until the lock clicks and the back end of the cover is flush with the side of the device.

B. If the cover is round and fits flush

1. Press hard around the edge until you feel some give under your finger.

2. Hold the pressure and rotate counter-clockwise.

3. To refit, study the edge of the battery compartment and the underside of the cover. Match them them and apply pressure, then rotate clockwise.

C. If neither of the above works

1. Inspect the sides of the device, pressing to see if the plastic is thinner and more flexible at any point. Press hard when you find the spot and insert a small screwdriver to keep the clip open, using the minimum force.

2. On the other side of the device, there will be either a tongue fitting into a slot, in which case the two parts have already parted, or a similar bendy clip as the one you have a screwdriver marking directly opposite. Insert another small screwdriver to press the clip inwards.

3. Refitting is the reversal of this procedure, with the two parts clipping together with minimum force against the weak battery spring.

Good luck.

An inner cover and an outer cover?  Inner cover, I would expect it to have a slot if it is supposed to be rotated, or an arm that sticks out to one side.

If you have the model number, perhaps the instructions are out on the internet?

Hi folks.
Last month I replaced the battery in the wheel sensor and today there's a blank screen on the main body.

I removed the outer cover but cannot flip off the cover over the battery itself.
I've tried unscrewing it but there's nothing to grab/ grip.
Nowhere for a screwdriver to fit in.

I hope the picture explains my situation.

I think old age has worked it's magic.

Any thoughts or tips much appreciated.

Matt

...
I did once destroy a new rim by inflating a 50 mm wide tyre to about 80 PSI. My idea was to use overpressure to properly seat the tyre beads on the rim. Doing that also destroyed the inner tube, but the tyre survived. ...

Thorn recommendations for maximum pressure in a rim have changed over time.  Last time I saw some numbers, I thought that the recommendations were a bit too conservative, but rims can be weaker than tires, especially if the rim has had brake wear and if the rims are corroded.

I wish all rims came with labels on them with that data.  My (now twenty plus years old) Mavic A719 rims did, photo attached.

I think I have put up to 60 psi in a 50mm tire, but not more than that.  I might have put 80 psi into a 40mm wide tire on the rear wheel of a touring bike with a heavy load, that was a really solid rim that was designed for touring, the now discontinued Salsa Gordo rim that I have on my Sherpa.

I think I have put 50 psi into a 57mm wide rear tire with a heavy load, that would have been the Andra 30.

I did a quick google search, found this:
https://thorncyclesforum.co.uk/index.php?topic=13100.0

And I posted this a decade ago:
https://thorncyclesforum.co.uk/index.php?topic=11833.0

ERTRO and Schwalbe are in effect saying, If you choose rims that are narrower than 40 percent of the width of your tyres, you'll have to inflate to a higher pressure to keep your tyres on the rims, which could lead to a catastrophic failure of the rim.

I did once destroy a new rim by inflating a 50 mm wide tyre to about 80 PSI. My idea was to use overpressure to properly seat the tyre beads on the rim. Doing that also destroyed the inner tube, but the tyre survived. The rim was a Gipiemme Mount, so I didn't buy any more of those.

If it is necessary, I now use Schwalbe seating liquid (or washing-up liquid) to seat tyres properly on the rim.