I picked up two of the $5.95 OEM batteries from eBay for around $23 including shipping. My phone has been off charger for 25 hours now and I'm still at 70%! The new battery combined with setting it to stay on 1x (no EVDO here) and changing the ActiveSync to not snyc on every receipt (now syncs every hour) has given me much longer battery life than I have EVER had.
