Is there any risk when battery packs are connected in parallel?
The main thing about parallel batteries is the double capacity. It's actually not really cool to put a new battery in parallel with discharged (me thinking about small me now replacing only one battery out of two everywhere lol). The charged (higher voltage) will try to discharge into lower voltage battery, and its chemistry is not designed to be rechargeable. I wouldn't really care much about them failing, never seen anything like that. I would say AA/AAA discharge two quickly in case of some short circuit (don't forget about internal resistance too). So yeah, put a new one with another new one so that voltage difference between them is minimal, and you're pretty much safe.