Ok, use same proportions of fruit and sugar as for normal berry pan jam. I used less sugar as I don't like my jam too sweet. Not many types of berry need extra water but I put a couple of tablespoons in the bottom of the bowl then put the berries in.
Leave the slow cooker on low with the lid on for about 4 hours, switch off and stir in sugar, leaving to cool till sugar is melted (I left it overnight). Then put cooker back on low after stirring well to make sure sugar is dissolved. I left it for a morning like that. Then take the lid off, cover with a dry cloth (tea towel) and leave for another couple of hours. You could test for setting then and jar up, or do what I did switch it off and forget about it
I jarred mine cold after sterilizing the jars and lids in the dishwasher. I have absolutely no idea why it has gone a gorgeous red brown colour as it doesn't taste in the slightest caramelized or burnt
The second lot has just been done in the microwave so I'll see how that turns out - it's still green!