You can double the battery life expectancy by discharging only 50% of capacity instead of 75%; you get 6 times the battery life at 30% capacity usage per cycle.

Think of battery lifetime as having $1000 in the bank and withdrawing a dollar with each 50% disharge cycle -- and withdrawing $10 every time you deeply discharge the battery. 

Life Cycle:  Generally accepted is 400 discharges to at least 80% DOD

Discharge Rate: 

Deep Cycle:  Designed to repeatedly be run down fully and recharge without being ruined 

D.O.D. – Depth of discharge 

     Lead Acid battery(deep cycle):  

       -  rated at 400 charge cycles at 100% 

       - will give 500 charge cycles at 80% D.O.D 

       - will last almost indefinitely if it is seldom discharged past 20%

Rules of Thumb: Range is proportional to battery size; twice the battery size = twice the range. When speed increases, range decreases even faster; 1/3 faster = 1/2 the range.  A 400-watt motor takes an average rider up all but the steepest hills.  One of the few parts that needs replacement is the batteries. Depending on the setup of your electric bicycle you will need to replace your battery every 1-5 years. 90% of bikes today use sealed lead acid batteries, which cost about $45 to $99 to replace. They are good for up to 300 recharges. Some use NiMH, (400 - 600 recharges) NiCad or even Lithium-ion, those batteries can cost as much as $400 but have 3 to 4 times the life of a standard battery. Some of these exotic batteries weight less than 1/3rd of the lead acid type. Also, some bikes may ship with lead-acid, but can be upgraded to Ni-Mh (need a Ni-Mh charger also) at a later time if you desire.

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