Stu

It's not whether the battery can take it but more if the charging system can cope 
 
The sat nav and phone will take next to nothing but the grips would be the higher drain
 
Your bike should more than cope with that 

I suspect that the specs are the recommended specs in the manual 
 
I would never go for smaller but nothing to stop you going larger 
 
Although the battery needs to fit in the holder and also have the correct orientation for the terminals 
 
Having said that I would get a battery that is recommended for your bike rather than trying to find one to fit 
 
Yuasa and Motobatt are good batteries you usually find motobatt specs are higher than recommended and their cold cranking amps is better 
 
AH is how much the capacity the battery has not how powerful it is cold cranking amps is the one to look at