A general answer is that you can expect to replace the battery about once a year.
A realistic approximation of a LiPo battery’s lifespan should consider both its number of charge cycles and its age (as well as proper use and storage.) In any case, a LiPo battery is deemed to be past its useful lifespan when its capacity has declined to about 80% of its original capacity.
While it has an average of 150–250 cycles (charging and discharging is one cycle), a LiPo battery is considered to start “aging” the first day that it is activated. This is applicable whether the battery is under regular use or is stored for a more extended period.
How a LiPo battery’s performance deteriorates during storage is determined by its storage conditions. See: Storing the LiPo Battery
A LiPo battery nearing it's expiration point will probably show signs of swelling or puffing.
Swelling of LiPo batteries happens due to the gas generated by the decomposition of the battery’s electrolytic solution. Aside from having significantly reduced performance, a swollen LiPo battery also has a much higher chance of catching fire when it overheats.
LiPo batteries use an electrolytic solution composed of a lithium polymer that is more gel-like in texture, which naturally tends to decompose over time, producing gases such as oxygen, carbon dioxide, and carbon monoxide. Gas production explains the swelling or puffing that many batteries typically experience when they get old or are poorly handled.
Performance will decline or stop if the battery voltage is allowed to drop below the 3.2v per cell - we recommend stopping to recharge before this happens as you risk permanently damaging the battery by over discharging.
CAUTION: The battery should always be allowed to come to room-temperature before charging. Charging a hot or cold battery might delay charging or damage the battery. For best results, charge the battery at temperatures between 50º and 80ºF (10º-30ºC).
Disclaimer
The advice given above is general in nature and you are responsible for the safety of your batteries. SwiftPaws is not responsible for any direct, indirect, special, or consequential damages and personal injuries, including that to life, and health, resulting from the customer’s application and use of batteries sold by SwiftPaws.com.