I was very pleased to find these instructions for acquiring and installing a replacement battery in my XL720.
The instructions were complete and easy to follow - better even than the author thought, as evidenced by his/her totally unnecessary apology for the quality of some of the pictures.
I had to wait a few days for the battery to arrive (I found a Canadian battery supplier:
Battery Buyer - Batterybuyer.com), but other than that, I spent a total of maybe 15 minutes disassembling the unit, replacing the battery, and putting it back together again.
I hope that others using this forum are as glad as I am that contributors like canderson sacrifice so much of their time to assist those of us who need it.
Many kudos and thanks!