If you are solely putting four hundred mAh or so into your 600 mAh battery, you’ll still only find yourself with the identical 400 mAh in there even should you go to a 900 mAh battery. As for the long-term degradation question, yeah, a battery that offers you two hours of run time new will usually provide you with less because it gets older. I don’t assume there is a good basic method of predicting that. I do not know sufficient about your system to know for positive.
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