I don't use a charger for now, but I remember having seen my XC90 with a charger when I picked it at the dealer. Connection were as shown on the instruction manual for jumps start and I assume it is the only correct way to do it.

 

You mean connecting the charger to #2 and #4 on your pictures ? I think it's 100% safe, but 10% convenient (having to open the hood to plug the car overnight...)

With my previous cars, I connected the charger to the battery in the trunk, so only had to open and close the hatch area to access it -which I think it more convenient than the hood opening...

I think I'll go with your option, though, since it seems very safe, but I'm curious how people here on the forum charge their batteries for the winter

 

The owners manual warns against using the battery terminals, the charging points under the hood must be used.
Volvo has a dedicated battery charger that is built in under the hood and has a power connection in the front bumper.
http://accessories.volvocars.com/en-my/XC90(16-)/InstallationInstruction/Pdf/VCC-474903-1/2016.
If I am not mistaken, it is quite expensive, perhaps due to the time it takes to install it.

 

I'd rather have that accessory than what I used to see on my parents cars during the winters (this pic is not our car, but we had the plug hanging out of our grill just like this): http://toolmonger.com/wp-content/uploads/2007/01/post-engineblockheater.jpg

I remember my parents would drive me to school and for some reason only the rear door would got stuck open. The front doors never had the issue.

No matter how many times I slammed the door, it would bounce open it was so cold (the door latch would sieze and not catch). There were many times when I had to hold my rear door closed while my dad was driving and wait until the door latch warmed up enough to latch and stay shut. Eventually I started using a skipping rope to tie the two interior door handles together so I didn't have to hold the door closed anymore b/c centripetal force would pull the door open while I was holding it when we went around corners. Good times.

 

A few years ago one of my vehicles wouldn't start on a -20 F morning. It was facing the wrong way in my driveway and blocking my other car, so I couldn't jump it myself and my neighbors had already left for work. After replacing that battery, I bought a Schumacher charger with multiple functions - jump starter, charger, conditioner and float charger. Now I charge my batteries overnight once per month. It must be working because the original battery in our previous Q7 lasted eight years through hot summers and cold winters. My procedure with the XC90 is:

-Open the hood, connect the charger to the terminals and plug it in.
-Select battery size and type to start automatic charging.
-Charger displays status and usually reaches 100% within 30 minutes, at which point it automatically switches to float charging.
-Unplug it the next morning and repeat in 30 days.

Supposedly the charger also "conditions" the battery when it detects that it is necessary. I don't know what conditioning entails, but I can't argue with the results. This process is easy with a garage, but I've also done it in my driveway with the hood lowered but not latched and the car locked while the battery is charging. Charging every 30 days has worked well for me. If daily charging was necessary, I might install an onboard charger like you are considering. But in my experience even South Dakota weather isn't bad enough to require that. Another route would be to install a pigtail only in the vehicle with the detachable end located somewhere you can reach without opening your hood. I see plenty of those in my area. Something like the Battery Tender Plus that comes with a detachable pigtail you can leave attached to your terminals.

I also keep a Micro-Start Sport battery pack in the rear cargo area that I charge every 30 days. You can't access the area underneath the cargo floor when your battery is dead (because the rear hatch locks it in place and can't be opened manually), so storing jumper cables there won't help you. You can't open your glove box with a dead battery either, so keeping a small jump start battery pack in an accessible location seems like good insurance.

 

I do not use a battery tender on my Volvo, except when loading road maps. However, here is a decent one that has a quick disconnect. I use this for other applications. I am not sure about the CA exclusion. There might be a CA-specific version. http://www.batterytender.com/Dion/Battery-TenderR-Plus.html

 

I have two of those Delton Battery Tenders. Great charger... LOTS of people on various forums use Deltons. I have one on my BMW 540i right now. Our XC90 probably won't get drive that often, so we might stick a battery charger on there as well.

 

I have a Charge-o-mat (CTEK Sweden AB) that I use when I store my Porsche Panamera. It plugs into the cigarette lighter.

Any comments on using this while updating the navigation maps on the xc90?

 

I have a Charge-o-mat (CTEK Sweden AB) that I use when I store my Porsche Panamera. It plugs into the cigarette lighter.

Any comments on using this while updating the navigation maps on the xc90?

The charger might not be able to keep up if it takes 2 hours for the map update. You'll probably not drain your battery completely, but it could decrease significantly. I have a CTEK MUS 4.3 POLAR for my M3 that's stored for the winter so I'm basing the charge rate on that.

Make sure you completely turn off the headlights, interior lights, AC/heat, heated or ventilated seats, radio, and anything else using the battery. You're better off starting the map update when you're driving for a long time and then leaving the car on at your destination to complete the update. I'm not sure if it's actually correct, but when idling our T6 says it uses 0.2-0.3 gallons per hour so at most you'll be wasting 0.6 gallons with the benefit of charging the batteries.