That issue has been around for sometime now. It will show you at 5% when you are really fully charged.
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Yes I have glad the same problem twice. Glad to hear it wasn't just me.
I have found that some kernels will make the phone "appear" discharged when in fact the phone has a full charge. I am running (currently, subject to change) Blackdroid's Froyo eXtreme (RC2) and I have tried putting on faster Kernels (1.25 GHz by ChevyNo1), but any new kernel introduced causes my phone to go batty (i.e. constant reboots, FCs upon boot, staying in stock "M" boot loop). This is not meant to endorse BlackDroid's version of Froyo, but rather just to state facts I have seen with this Froyo Kernel.
FWIW, I have also tried other flavors of Froyo (Pun intended) and found Froyo to work well. The voice Dialing via BT is not the best (and is actually one of the worst, but it's a step in the right direction). I have tried "calling mom" only to have the phone say "Calling John LastName" or other such snafus.
Cheers,
B.D.