Due to some fairly tight physical constraints, I need to use a fairly small battery for my RTC. 20mm, 12mm and even 10mm are all too large and I'm looking at using a 6.8mm ML621 which is a rechargeable 5mah. Rough calculations suggest this should last around 100 days for the RTC, which is fine as this will rarely go 100 days without use, but means I need to ensure that I can charge it when the unit powers on.

Panasonics recommended charging circuit is fairly straight forward, just a Schottky to drop the voltage (Max charge voltage on the battery is 3.2v) and a resistor of specified value, so I was hoping to use something like this
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I know there is a diode already on the 3v3 -> VBat line though and just wanted to make this wasn't going to interfere with anything that's already happening on that circuit. Does this setup seem reasonable?