Icom A20 not works with battery

Hello,
I'm carrying an Icom A20 that works well with external power supply from the upper connector (and charge the battery at the same time) and works well when it conected to the conector on the battery package . The issue is that the Transciver dosent works with the battery (good battery) alone.
Please advise.
Sencerly,
Gideon
gideon_asher@yahoo.com