please help,is this board or battery problem?

Hi so i have JBL Xtreme 2,not the 3,cz theres no JBL Xtreme 2 in the selection page,
the problem is,the battery seems dead,and four of the lithium cell seems dead (0V),i dont wanna buying the battery cuz the battery price are almost as the speaker unit itself lol.

uhm,the problem is,when i was connecting the speaker directly,it doesnt showing any sign,but when im connecting the dead battery,the speaker blinking red and looks like low battery,JBL Xtreme battery mod doesnt work because it have 6-battery pinout (Red-Red-Yellow-White-Black-Black),and i cant use the speaker right now,

while checking the voltage,it seems charging the battery with 19V itself,is this right?,because the battery specification are show 8.4V Maximum.

trying using the lower voltage (12V) adapter shows blinking red and i can powering on the speaker for just a sec until the speaker turn off like its low battery

this is weird problem

do i have problem with the unit?,because the warranty already void,
do i have someway to just use this speaker?,

is there any jumper way or replacement kit for the battery or what?,
theres no battery mod for jbl xtreme 2 on the internet

thanks for reading and replying,