Here is a list of common mistakes and how to avoid them:
Neglecting Shelf Life. Batteries have a limited shelf life which is exacerbated if stored at high temperatures. Additionally, quiescent currents may drain the battery.
Solution: Know how the battery will be used and stored in the application, and be certain communication from the battery draws the lowest possible current.
Not Leaving Enough Space. Not all "standard size" batteries are the same size; cells can vary as much as a millimeter in any direction. In addition, prismatic cells swell in thickness over time.
Solution: Leave enough room for the largest of cell sizes in that product category, and for prismatics, allow 10% additional room in the application space.
Disregarding Temperature Effect. All batteries have a limited temperature range; exceeding this range will reduce battery performance and life.
Solution: Either derate your battery's performance for applications that will be cooler or warmer than room temperature, or increase battery capacity to accommodate temperature changes.
Single Sourcing Cells. Cell manufacturers often design a cell size with a particularly large volume customer. If that OEM moves on to another product size, the cell manufacturer may discontinue that cell size.
Solution: Choose a cell size that is commonly used among the industry among a variety of vendors.
Omitting Cycle Life. Manufacturers specify performance to 80% of capacity at end of cycle life.
Solution: Expect shorter run time as the battery ages. Know the cycle life of the cell you are using, and consider derating capacity accordingly.
Miscalculating Charging. Proper charge methods can make the difference between a battery that lasts five years and a battery that lasts five weeks.
Solution: Ensure that your charge method is appropriate for the chemistry used.
Discounting Battery Behavior. Battery voltage drops as current draw increases. The problem is exacerbated with low temperature.
Solution: Ensure that the nominal battery pack voltage can accommodate for pulse currents and low temperature usage.