The battery tray in the Diesel Vanagon is a fair bit bigger than the BCI group 41 battery that is specified. Over the years I have used various other batteries BCI group 41,34,78, some 27.

Has anyone fit a group 65? It's a bit wider, so may interfere with the mounting.
For decent value batteries in Canada I have checked Canadian Tire and Walmart.
Any other suggestions for sizes and sources?

A 34 is a bit taller, but clears the engine lid if at the forward end of the battery tray. A cover on the + terminal is a good idea. Does not clamp as well w. original bottom clamp.
A 78 has side terminals, so not the above terminal issue. There's also combination 34/78
34/78 typically has 800 CCA or more compared to the 600 for a group 41.
Also a bit more reserve capacity.

Group 27 batteries seems to be the largest that fit the width and length. Height can be tricky. Depending on how the terminals are arranged these may fit or may not. The past decade I used a Canadian Tire Motomaster group 27 marine battery. This had 800 MCA, and 100Ah. That's twice the Ah of a regular starting battery. For marine use these are designed for both starting and house battery needs. This worked well in the Westy camper also. The extra capacity was also handy in  a trip wyhen the alternator failed, and we had to wait 2 days for a replacement. 

Now when I wanted to replace it I noticed the new model has much taller terminals molded into a palstic block that sticks out, so it won't fit. Therefore I'm looking for other alternatives. Therefore I was looking for other alternatives.

I was also wondering about the relative value of "premium" vs regular batteries. While a premium battery might be a little bit better than a regular, I was thinking most of the additional premium price goes not into the battery quality but to the longer warranty, roadside assistance and other perks. I was just considering flooded cells, not AGM.

Heres a listing what I found on the Canadian Tire and Walmart Canadian web sites:

The very high reserve capacity of the "Certified" group 65: 130min might be a misprint? Similarly the low 

Walmart batteries are apparently made by Johnson Controls. Some Canadian Tire Motomaster are Excide. Any one knows about the Certified?

http://www.canadiantire.ca/en/battery-charts/automotive-battery-chart.html
clickable link
BCI GROUP SIZE     PART NUMBER     VOLTS     COLD CRANKING AMPS AT -18°C     CRANKING AMPS AT 0°C     RESERVE CAPACITY MIN AT 25A     Ah CAPACITY (20hr)     LENGTH (in)     WIDTH (in)     HEIGHT (in)     TERMINAL TYPE

Certified: 1yy replacement 34/78 or 65: $119
group part
34/78DT     010-3472 >     12     690     850     110     --     10-3/4     6-7/8     8
65     010-6503 >     12     675     830     130     --     12     7-3/8     7-5/8
Motomaster $140-150 3 year free replacement
65     010-6500 >     12     850     1045     150     --     12     7-3/8     7-5/8
010-4100 >     12     650     800     100     --     11-9/16     6-7/8     6-7/8
010-3400 >     12     690     850     110     --     10-3/4     6-7/8     8
27     010-2772 >     12     710     875     120     --     12     6-3/4     9
27F     010-2700 >     12     710     875     120     --     12-3/8     6-3/4     9
34/78DT     010-3478 >     12     800     985     115     --     10-3/4     6-7/8     8

https://www.walmart.ca/en/ip/everstart-battery-maxx/6000195362544
EverStart Battery MAXX
Built for Canada Tough , Group Size 27N , 710 CCA 
$126.97
• 710 CCA
• 120 Minutes Reserve Capacity
• 5 Year Warranty program with 3 years free replacement
• Maintenance Free – never need to add acid
Justy top post no screws. May fit.

https://www.walmart.ca/en/ip/everstart-battery-maxx/6000195362483
EverStart Battery MAXX
Built for Canada Tough , Group Size 65 , 850 CCA 
$133.97
850 CCA
• 100 Minutes Reserve Capacity
• 5 Year Warranty program with 3 years free replacement

https://www.walmart.ca/en/ip/everstart-battery-maxx/6000195362498
EverStart Battery MAXX
Built for Canada Tough , Group Size 41 , 650 CCA 
$121.97
650 CCA
• 100 Minutes Reserve Capacity
• 5 Year Warranty program with 3 years free replacement

https://www.walmart.ca/en/ip/everstart-battery-plus/6000195362535
EverStart Battery PLUS
Built for Canada Tought , Group 78 , Dual Terminal , 540 CCA
$89.97
Dual Terminals – Both side post’s and top post’s
• 540 CCA
• 85 Minutes Reserve Capacity
• 1 Year Free Replacement Warranty