To understand how far a battery will drive your electric bike compared to another one, it's good to speak in terms of "flow per hour." You can ask, "ok, if these two batteries have electricity flowing out of them at a rate, or 'flow size' of 8 amps, how many hours will each of them do that until they are drained?" If one of the batteries could have electricity flow out of it at a rate of 8 amps for one hour before it was empty, we would call this an "8 Amp/hour" or "8Ah" battery. If another battery could last for an hour and a half while being drained at that rate, we'd say it was an "8.5Ah" battery.

One more thing you may consider when buying a battery for an electric bike or conversion kit is when you may want to replace it. No battery lasts forever, however, most rechargeable batteries will be able to be recharged many hundreds of times before they begin to wear out. For example, Clean Republic's Big Lithium (nickel-cobalt-manganese) battery can be fully discharged and recharged 500 times before its performance drops to below 80% of what it was originally. The standard lead acid battery pack in Clean Republic's standard Hill Topper kit is rated at 400 cycles. The two biggest factors to consider here are probably the total number of rated recharge cycles, and the overall price of a new battery. Under normal usage (say two full battery cycles per week) any Clean Republic battery pack will give you years of good service and performance. The price of a given type of battery may affect your decision at some point in the future when you want to purchase an additional battery pack to increase your range or replace your original pack altogether. The cost of a standard lead acid battery pack is generally much lower than a lithium pack. This is due to the higher production cost of the more complex chemistry and management circuitry in the lithium battery. Clean Republic offers a variety of options for new battery packs and lithium upgrades for kits with standard packs so that you can always have the battery features you want.

Lithium chemistry, power, and replacemen | Chapter 4