Leisure battery capacity

[Hog]

Just after some advice chaps - hopefully someone can point me in the right direction.

In an effort to become more self sufficient with my racing - and not having to keep scrounging the use of someone's generator to race - I'm looking at leisure / heavy duty batteries to keep me and my kids charged when we race outside.

Now both the kids are only running their SC10's with 13.5's so their battery use is not heavy. I tend to run 2 classes outside, SC10 and 4WD with 6.5's in so my use is heavier. Assuming we all practice, have 4 rounds and a final, what sort of battery capacity will I need to keep us going for the day? We use a PowerPal 4 way charger which makes things a lot easier.

I've got a 100A battery (800A cranking) which takes a good charge (and I've left it on one of these monitoring chargers) - will this be enough? Or do I need something specifically for a deep cycle? The battery I have I believe is off a tractor.

Thanks in advance.