Help with DS Lite repair - Water damage

Hi everyone, recently I tried fixing up my brother's DS Lite that had stopped working due to water damage a long time ago. When I try charging the DS the orange light briefly turns on then off. I cleaned any residue I found inside with some isopropyl alcohol and used a multimeter to check fuses F1 and F2, EM10 filter and charging port, all seemingly working fine. I came to the conclusion that the battery is fully dead, since I read that the light does that when no battery / dead battery is connected and due to it feeling kinda puffed up to the touch, also I coundn't get any reading off of it with the multimeter. Is there any way to be sure that the battery is truly the issue before I buy a new one? Thanks in advance!