Basically, you can replace the battery yourself.
The trick here is to use jumper cables to keep the cables on your battery powered.
Keep the jumper cables on a third battery connected to the cables to your battery.
When you disconnect your battery - the jumper cables and the third battery
will keep your rover powered up.

then when you put in the new battery, there was not a "no battery connected" event and you are set.

Personally, I would spend $110 for a battery at Walmart.
Will work just fine.