I've seen some questions about connecting batteries in parallel to increase capacity, and the answers all indicate that it's fine to do. But why? Isn't that creating a short if the batteries aren't at the exact same voltage? I understand there's some internal resistance in the batteries, but is that enough to make this safe?
Is there any benefit to isolating the batteries with diodes? E.g., give each battery it's own diode, with the positive terminal connected to the diode's anode, and then putting each of these battery-diode pairs in parallel?
I'm concerned entirely with off-the-shelf alkaline batteries, like AA, AAA, possibly 9V.
No, it's not ok in general, for the reasons I described in the question (creating a short circuit).