My main concern is will the Di2 battery be affected if the bike is stored at a low temperature without use for 10 – 12 weeks without regular use?

No, just charge it and stick it in your desk drawer, you’re going to have the same problem every winter if you don’t ride it anyway.

Secondly, if I leave purchasing the bike until spring, are the chances greater of my size being out of stock by then (Specialized)?

Not much unless it’s some sort of niche bike* that suddenly becomes an overnight success after a magazine review. So unlikely to sell out of Allez or Tarmacs, more likely something niche like Sequoia or Diverge.

Although you would probably get a much better deal buying a 2018 bike right now.

*Specialized Pitch and Cannondale Prophet when they were reduced to £999 as no one saw the point of 150mm travel ‘trail’ bike before Enduro was invented) then MBR gave them 10/10 and they sold out in weeks.

I am pretty sure Di2 stuff will sit in a warehouse over winter which are usually about as cold if not colder than your average garage/shed.

I f they could not withstand a bit of cold then they would not be able to sell them.

My di2 bike lives outside year-round.

Lithium Ion batteries should be long term stored at 40-75% charge in the fridge. So unless it’s actually below zero you are all good.

What kills modern batteries is:

– Deep discharge

– Overcharging

– Many charge cycles

– Charging while hot