Different capacity batteries in parallel?
i'm not an expert but...

"Most battery chemistries lend themselves to series and parallel connection. It is important to use the same battery type with equal voltage and capacity (Ah) and never to mix different makes and sizes. A weaker cell would cause an imbalance. This is especially critical in a series configuration because a battery is only as strong as the weakest link in the chain...

A weak cell may not fail immediately but will get exhausted more quickly than the strong ones when on a load. On charge, the low cell fills up before the strong ones because there is less to fill and it remains in over-charge longer than the others. On discharge, the weak cell empties first and gets hammered by the stronger"

you need only 1ah to run a 10watt load on a 12v battery. your 2ah will last 2 hours from a full charge if you use only that. if you need it to run longer then the 7.2AH would last most of the night.