To start, leave your dermal tool in the case. All you need is a heavy duty box cutter. And a little time. Run the edge of the seal with the Box cutter. Twisting up the box cutter a little at a time. You will feel the glue start to give. Once a corner breaks free, the rest is easy.
Step 1: Those Pesky Triangle Screws.
Find a small flat blade screw driver tip that fits against one side of the triangle. Comes off no problem.
Step 2: Wiring It Up.
Before disposing of the old batteries. Cut the battery terminals off. Now I used a 10 amp fuse holder in the circuit. These can be found at Walmart in the RV lisle. I also used RC type Deans connectors for the battery. You can forgo most of the Deans plugs except for the battery connection. You need a way of charging the battery.
Step 3: Putting It All Together.
It's a 1500 Mah LiPo 4 cell battery, 16+ volts. It all fits nicely with room to spare. They make a battery alarm that fit the balance lead that will fit in the case. It will alarm once a set volt per cell is reached. LiPo's don't like to be over discharged. They can be dangerous if not treated with care. Do not run the Roomba unattended. You have been warned. The down side to this hack is you have to remove the battery for charging. A fast charger will top it up in less than 45 mins. Replace the triangle screws with conventional ones. It ran my roomba for 30 mins, with 15+ volts left over when tested.