Lumia 640 LTE Only Show Red Battery Sign

[Windows Central Question]

Last night, my on-charging-for-an-hour Lumia 640 LTE (1) suddenly cannot boot. It's only show microsoft symbol and then goes black, and on and on. When I plug off the battery (A) and plug in it again, it goes on red battery sign.
I, then replace the battery with my other Lumia 640 LTE (2) battery (B). It's finally on but saying my device has been locked for security reason. I plug in the battery (A) to my other Lumia 640 LTE (2), and it goes to red battery sign too.
Is it the battery (A) faulty? It's only a month from the day I purchased it, and I rarely used it.
Note : I used battery (B) on my Lumia 640 (1) to do the update and it goes fine. Trying to put in battery (A) on Lumia 640 (2) again, and it won't start.

 

[Chintan Gohel]

Last night, my on-charging-for-an-hour Lumia 640 LTE (1) suddenly cannot boot. It's only show microsoft symbol and then goes black, and on and on. When I plug off the battery (A) and plug in it again, it goes on red battery sign.
I, then replace the battery with my other Lumia 640 LTE (2) battery (B). It's finally on but saying my device has been locked for security reason. I plug in the battery (A) to my other Lumia 640 LTE (2), and it goes to red battery sign too.
Is it the battery (A) faulty? It's only a month from the day I purchased it, and I rarely used it.
Note : I used battery (B) on my Lumia 640 (1) to do the update and it goes fine. Trying to put in battery (A) on Lumia 640 (2) again, and it won't start.

from your experiment, it does look like the battery is faulty. Since it's been less than a month since you bought it, you can take it back for repair or replacement. Warranty should apply