I recently added a front hub motor (250W 8Fun brushless geared) and 36V 12 Ah Lithium-Ion (LiMgPo4 made by Beyonderpower) to a Giant Cypress 4 Hybrid bike. The Motor/Battery and controller all came in a Kit from a Ebay seller. The Kit included Twist throttle, Pedelec sensor and brake levers with switches to turn off motor (which I didn't install as my brake and gear levers were combined). The cost of the Kit was A$375 + postage of A$79. I had purchased the bike for my son a year ago for A$399. Total cost A$853.
The kit was reasonable easy to install althought I did have to grind a bit of metal off the inside of the steel front forks which was hitting the hub motor. I didn't install the brake switches and feel they are not neccessary unless you have a regenerative braking system or a cruise control throttle.
The bikes mass was 15.8 kg before conversion and 24.8 kg after, including battery (20.4 kg with battery removed).
The longest ride I have been on is 50km (with pedaling) with the battery leds indicating 1/2 full after this ride. The Battery charger took 0.4 kWh of electricity to replenish the battery after this ride. I believe a 36V 12 AH batter should hold 432 (36x12) watt hours of electricity and be able to run a 250W motor for 1.7 hours.
The Hub motor doesn't add any power after about 28 kph. The hub has almost the same resistance as a normal front wheel hub when freewheeling. However, even this relatively low power motor which is just over the maximum allowed in Australia (200W) really transforms my ability to climb hills. Today I rode from sea level to 420 meters elevation over 10 km without stopping. I have done this before once without electric assistance on my lighter (10kg) road bike and it was a hugh effort with 3 or 4 stops.
Yesterday I rode the bike to work 18km each way and reasonally flat and was able to survive with a towel sponge clean up and change of cloths rather that having a shower which was needed after riding my non-electric bike.
I am very happy with the bike. I am much more confident to tackle big hills and I am now able to venture along many new tracks which were previously too hard.