Sorry for bad english, I used google translate.

I bought a tello a month ago, I was happy but my flight time is now very short. With my fully charged battery I can fly for 5-6 minutes, what could be the reason? The backup battery is not possible to buy very expensive in Turkey.

I put two light rays on it, but even in this state it was flying for 10 minutes. Now I don't think the flight time has anything to do with that.
Charge increases from 100% to 90% within 1 minute, even before you start flying Tello.

This is my tello;

Dear, the normal status of charging indicator should be blue and it blinks once per second regularly and periodically, when the charging is finished, the indicator turns into solid blue. If the indicator is not the status aforementioned, such as blinks quickly, please try with another adaptor of 5V1A-5V2A or Micro USB.
If the problem still persists, Please contact us via support@ryzerobotics.com.

As for flight time, please test with a fully charged battery and do it indoors with a temperature approximate 20℃, take off the drone and keep it hovering until critical low battery to land automatically. If the flight time can reach 10 minutes and 30 seconds, then the battery is normal. If the time is less than 10 minutes and 30 seconds during warranty period, it is suggested to send the battery back to repair center for a further examination, please contact us via support@ryzerobotics.com.

Hope my response could help you!

RYZE Posted at 12-20 19:17
Dear, the normal status of charging indicator should be blue and it blinks once per second regularly and periodically, when the charging is finished, the indicator turns into solid blue. If the indicator is not the status aforementioned, such as blinks quickly, please try with another adaptor of 5V1A-5V2A or Micro USB.
If the problem still persists, Please contact us via .

When I removed the lights I installed under it, my flight time increased, even when not flying, the charge decreased but now the problem is solved

Kalipsotr Posted at 12-20 23:37
When I removed the lights I installed under it, my flight time increased, even when not flying, the charge decreased but now the problem is solved

Dear, we are happy to hear the good news.
Please notice that the drone is tiny and it is not suggested to carry any third-party accessory.

Maybe try flying it in less wind, because faster wind can cause the tello to use more power.  Or maybe fly in warmer weather, I found that in the winter the batteries drain fast.