Ford focus 2000 1.8 petrol lights on chimes on start up?

When I start my ford focus after it's been stationary for a while the lights on the dash are quite dim and the lights on chime 'dings' a few times but she does start first time.
I've not heard the chime before on start up! I've checked the belts are working and all appears ok under the bonnet.
Could it be the battery? Alternator?
Please help. MOT due next month so I'm expecting a big bill.

Make sure gas cap is tight

It wouldn't start this morning so I assume it's the battery. Just hope it's not the alternator.