Good information from GG. At the very least, you need a meter so you can measure the voltage of your batteries. A fully charged single-cell lipo should measure 4.2V. If it's less than that after charging, either the battery is defective (or worn out) or there is a problem with the charger.

If some batteries, such as your TP, come off the charger measuring 4.2V, then the charger is probably OK.

Even a $5 meter will do the job of measuring battery voltage. However, you can learn even more with a proper wattmeter that you place inline with the battery while running the motor. The wattmeter will show you both voltage and current, so you will be able to tell if battery voltage is dropping too much under load and if your motor is drawing more current than it should.

Generally speaking, a brushless motor doesn't wear out and draw more current as it ages, unless the motor has overheated. Overheating can damage the magnets, at which point the motor will usually start drawing more current. Brushed motors, on the other hand, definitely wear out and often draw more current as they get older.

In summary, get at least a cheap meter so you can begin to determine what is happening.

- Jeff