These small wooden barrels can have a useful lifespan anywhere from 1.5-2.5 years depending on the barrel size. Larger barrels will last longer as they have thicker staves and a larger charred area, some of the larger barrels can last 3 or even 4+ years.
As the barrel is used the charring inside will start wearing off and thus imparting less and less oaky flavor and brownish color to the beverage. Aging wine seems to reduce the charring faster as the wine tends to impregnate the wood covering the charring.
*Note: You are able to continue to use the barrel but with the minimal aging effect.
Unfortunately, there is no easy way to re-char the barrel to extend its life. The lids must be removed to char the staves and it can only be done with larger barrels as with each charring the stave thickness diminishes making them weak and susceptible to breakage.
After their useful lifespan in addition to no longer being able to age liquors. The wood may start to crack, remember wood can only hold liquid for so long until the liquid slowly starts causing the wood to decay.