In September 2011, my wife noticed the voltage dropping into the 20s (48v NiMh battery pack) while going uphill. After discussing this with Justin at ebikes.ca, decided that the old battery pack (3 years old) was nearing the end of its useful life (we got 261 cycles, 1034 Ah, and 2850 miles of it).

Looked around and found an acceptable replacement battery (LiNMC) at Chicago Electric Bicycles thru Amazon. The battery arrived within a few days. I was able to re-use the old Anderson terminals from the old battery pack, so it was easy to connect to the eZee wiring. The battery working out well, with a fast recharge and much lighter weight (old=22 lbs vs. 7.8 Lbs for the new). Losing 14 lbs on the rear rack has done wonders on how the bike handles. Also, the new pack is claimed to have better thermal properties (better heat management), so it will be interesting to see how this works out this winter and new summer.