Soldered to the main board. Hold your iron on the connection for a second or two to soften up the old wiring and remove. Then pre-tin the ends of the leads on the new battery, heat up the connection on the board, and set the lead in place. Or you can snip the wires off the old battery, leave yourself some room to work and just solder the wires of the new battery to the old battery. I snipped the wires and soldered the new battery to them. The battery pack is a generic phone-style unit. Word of warning, the tiny T5 screws are as soft as butter, even though they are only screwed into plastic, easy to strip the heads out. You could also compromise the waterproof rating of your unit opening it up. There is a thin, rubbery/sticky seal around the edge when you pull the two halves apart. I considered this a $20 experiment, as the PTB was pretty much useless with only 2hrs or so of runtime. If it gets me another year or so, I'll be happy.