The 1800mAh is 2.3mm thicker than the regular battery, which from a practical point of view is not a big difference. I have that battery, which lasts nearly twice as long as the standard 1100 battery, as well as the standard Sena. They are a wonderful combo.
At one point, before I bought the 1800, I wanted the 2200. I decided not to get it b/c it's 1/4" larger than the standard battery. That's a big difference and would be too bulky for a stylish man like me

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In my humble opinion, a pda should be small and portable. The 2200 battery with the extended metal case makes it too bulky to be called a pda. It should be called a Newton or something with that extra size.
Good luck with your decision.