Thanks guys, I had forgotten that the rechargeable could be swapped for ordinary AAAs. I would imagine it takes four AAAs which I will get tomorrow as it is now 9.25pm as I input this.

If it proves that the rechargeable battery needs replacing I'll have to decide whether it is wise to go that route or bite the bullet and invest more cash in a new unit as I would hate to replace the rechargeable and then find that the Pronto fails in another area not too far in the future.

Once the batteries are installed, I will probably have to wait until Thursday evening when the unit will be cool enough to test this theory out.

Watch this space

Cheers
Caroline