Two 3.6v camera batteries in series?

Hello battery guys! I got a question, thanks for taking the time to read and respond to this. I've done many a google search, but no luck.

Is it okay or bad to use (and charge) 2 3.6v camera packs in series?

Here's why: I have a space-demanding application in my next product, (0.675"x3.8") which needs 7.2v. All my other designs use off-the-shelf camera packs + smart charger. But I cannot find an off the shelf 7.2v pack to fit in this space, they all seem to be side by side cells, where I need end to end. I've put in RFQ's to a couple of companies for custom packs, but I was wondering about this as an alternative. Does a single protection PCB knowing about 2 cells enhancce safety? Or does 1 PCB per cell work ok?

Thanks guys!

Tom
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