welcome, for my money, i would only buy a battery operated circular saw if you are away from power, ie not very often on most jobs in the home. they are ok at a pinch say of you are working on a roof, but the benefits and power of a mains powered circ saw far far outweigh those of the battery version in 95% of scenarios.
if i were you, i would be considering the reciprocator saw and a pack of decent spare blades, THATS a tool you will get a lot of value from around the house when doing DIY work.
good luck