Paul,
No I don't know of them other than what the internet tells me. I assume they are in your van - did you put them there? If so, why?
Generally Marine batteries have a smaller "Deep Cycle" capacity than AGMs as they have the "start" facility as well - I've used marine batteries as an aux battery in the car as they are lighter & slightly smaller (80Ah vs normal 100Ah). Most marine batteries are of Gel construction, these days. Calcium batteries are Gel batteries with a calcium compound as the frame material.

You SHOULD use the correct setting on your charger if you have it. Calcium (Gel) batteries, like AGMs have to be taken up to 14.3-14.5v (higher than what a lead-acid battery needs) if you're going to get a good life out of them. See www.energymatters.com.au/components/battery-voltage-discharge/

Calcium calcium batteries require a higher charging voltage, any where up to 15v for some brands. the advantage is they start from a higher voltage when fully charged so their actual watt hr storage (Wh) is higher than a lead only battery of the same weight. they are really only useful for high current short duration discharges such as starting or winch operation, not really designed for deep cycle use. No doubt the price was better and most people wouldn't know one type of battery from another, so they have probably been getting away with this practice for a while. I have seen this practice from a number of caravan manufacturers and when challenged they all claim It was a mistake" and they replace them with proper deep cycle batteries. Others have arrived at our door for a battery upgrade anyway, so they just roll their eyes and it doesn't seem to surprise them at all.

T1 Terry