I just did a replacement of the battery in one of my Behriner MPA100BT portable active PA Bluetooth speakers. So i made a short step-by-step guide!
The battery has to be in the exact same form factor due to a tight fit. Some motorcycle batteries might fit but often has different poles, UPS batteries might be easier to get in this style. The battery has to be 12V, and the included one is 8Ah.
This is the one I am using: https://www.kjell.com/produkter/kontor/batterier/blyakkumulatorer/yuasa-blyakkumulator-12-v-85-ah-p32885
The first step is to take out the back-panel. Start by screwing out all the 8 screws marked with red circles on the picture below.
Lean the panel out and disconnect the white connector with red and black wires coming from the battery.
This may have some glue on the side that need to be removed.
Inside the speaker remove the 4 screws marked with red circles below and take out the two mounting brackets for the battery.
The battery is sitting tight, use the belt around it to drag it out.
When the battery is out remove the red and white wired from the battery. This is done by sliding the plastic on the cable up and pressing a release point on each pole.
Set in the new battery with the same cable and do the whole process in reverse.
Now just charge the battery up and you are good to go. Easy.