Wife took the car in this morning for its 80 000 Km service. Was in for 3 hours. Apparently they did a stellar job and even washed it and hoovered inside - in 21 years of living in Finland, i've never had that done on a service.

Apparently brake pads need changing - 4 hours worth of work.
The 'battery low' message which i've previously mentioned - which was directed as being the Stop /Start battery that hates the cold (we just had -27 for 36 hours) - need to charge this battery. and if that doesn't work then replace the battery.
Am i correct to assume that the Stop / start battery is behind the side panel in the boot. I have a CTEK charger, can i just connect directly to the terminals or should i remove it? (bearing mind it's bloody cold here)

On a positive note, the wife had a new RRS Hybrid for the 3 hours that the service lasted. and thoroughly enjoyed it. So much so that she came away with a part exchange offer for ours [which we only bought in April] and she booked in the brake pads to be changed next month, and it will take 24 hours, so we will have a Hybrid again, but for 24 hours this time.

Oh and the service was a snip at 1300 EUR  2019 RRS P400e Autobiography
2014 RRS 3.0 TDV6 HSE Dynamic
2006 RRS 2.7 TDV6 HSe
Alfa Romeo Guillietta 2.0 JTDM 2011
Mazda 3 1.6 2010
Subaru Impreza 2.0 WRX 2005

I connected my CTEK straight to the terminals on the stop start battery whilst it was in place - as you state behind the panel in the boot on the right hand side - no issues at all Be aware if you do remove it be careful not to over tighten the terminal connections when replacing - they are not as strong as the normal battery & the lugs break  16MY Estoril Blue SVR.............
17MY Autobiography Dynamic - Corris Grey - WOW.
14MY Autobiography Dynamic - SDV6 - Fuji White
12MY Autobiography - SDV6 - Santorini Black - Dual View - Rear Entertainment - Sunroof.
12MY Autobiography - SDV6 - Orkney Grey - awesome ;(
2005 Java Black - 4.2 V8 Supercharged First Edition- will never be forgotten ;(

That was a bargain for servicing, not The wash & hoover was probably 200 euros
Anyway on to your stop/start. You can read my long winded posts if you have nothing else to do but here is the abridged version.
Firstly because there is a battery management system, you do not attach your Ctek to the battery. Attach to the connections under the bonnet. There is one connection under a plastic cover left hand side in engine compartment +ve & a stud for -ve
I had new batteries & still got low battery warning. I was using Ctek MKS5, charger seemed fine but still got warnings. Noticed Ctek had a CT5 Stop/Start charger so bought one, connected it up, left it for a day & stop/start worked. Unbelievable, after months of trying different things
One thing, as you are in Finland where the systems have to work a lot harder, ie lights, heating, defroster, heated seats etc, the stop/start is overridden if the car senses it needs too much electrical power, so this may be your problem & there is nothing you can do if this is the case.
I found the main dealer was worse than useless when I mentioned this. Their reply was, get a new battery, it is a new battery I said, oh well use the car more, Total waste of time

Thanks, that's pretty much what i figured. heated seats, heated steering wheel, heated windscreen and wing mirrors, plus the heat to heat the cabin, radio, iphone plugged in.
And then the Stop / Start won't work in so low temperatures anyway.
I did tell the wife all of this already a while ago, but she doesn't sometimes hear the sound frequency known as 'husband talking'

Will get the CTek on tonight to the points under the bonnet first as that will be easier.

cheers 2019 RRS P400e Autobiography
2014 RRS 3.0 TDV6 HSE Dynamic
2006 RRS 2.7 TDV6 HSe
Alfa Romeo Guillietta 2.0 JTDM 2011
Mazda 3 1.6 2010
Subaru Impreza 2.0 WRX 2005

Incidentally the wife came back with a trade in offer for the Hybrid.
We bought ours in April 2018, for 86 000 EUR with 69 000 km on the clock.
It now has 83 000 km

Thy hybrid would have 5000 km driven and is the same spec as ours except In Control Touch Pro, keyless entry, keyless boot entry and timed climate.
115 000 EUR, but he'll give it to us for 108 000 EUR. The trade in price on our car would be 50 000 EUR. a loss of 36 000 EUR in 10 months....... 2019 RRS P400e Autobiography
2014 RRS 3.0 TDV6 HSE Dynamic
2006 RRS 2.7 TDV6 HSe
Alfa Romeo Guillietta 2.0 JTDM 2011
Mazda 3 1.6 2010
Subaru Impreza 2.0 WRX 2005