this is the tricy part.

the new pack should be facing you with (+) (-) (+)

solder the right (+) to the (-) in the middle

Lolder the upper left (-) to the (+) in the middle

I used some old wire for it

Now solder the short black wire to the upper (-). It must be the only (-) with no connection yet

Solder the red long wire to the lower left (+). Also this must be the only (+) left without any connection

let it cool off