strange problem when using power ,maybe alternater

now that the mornings are getting darker im using the lights and heaters etc , i drive 2 miles to work and when going down to tickover the revs drop and the belt or 1 of the belts starts to squeel i cant rev through it either
ive checked the belts and there tight?

Belt tensioner or alternator bearing perhaps? Pulleys and belt surface shiny so slipping under load.....

Try some talc powder on them as thay may be worn and shiny and may even be cracked on the inner side

Also as your doing a short journy you may be drawing more out the battery than the alternator can put in on a short journy

The belts are worn replace them as no amount of tightening will help!
Having said that your main problem is your short journey!
The battery isn't getting charged up with everything switched on also your battery might need replacement??
If it's anywhere near 4 yrs old get a new one before the winter starts.
Check the other problems first and if it still happens then you'll need some sort of trickle charger.
I've not tried one but possibly a solar charger in the windscreen/dash might help but your main problem is the short journey!! Get a bike