How long do portable chargers last before needing replacement?

Quality lithium polymer batteries last 500 1000 charge cycles before significant degradation. With daily use, expect 2 3 years of good performance. After that, capacity gradually decreases a 10,000mAh battery might only deliver 7,000 8,000mAh. Signs it's time to replace: noticeably fewer charges, slow charging speed, swelling, or excessive heat during use.