If you want to be by the book, you change out the 810LED for a 48V version, 4 pin version.
1.24V or 36V or 48V Display. Cable Length:140cm.
www.ebay.com
This will allow the electronics to shut down the bike when the battery reaches 40V, The bar graph on the 810LED will also be a bit more accurate for the voltage too.
It will run on the 48V without doing anything. but the old LED display will let the bike run the 48V battery down to 30V. The battery should have its own low voltage cutoff, which will trigger before it gets that low, Nonetheless,if it's allowed to hit the battery cutoff,that's hard on battery life.
Note that ebay is full of offers for the 810LED 5 pin version. That won't work with the Ecotric controller. You have to get the 4 pin and specify that it's 48V, However, unless you already have a 48V pack as a spare, if you're going to buy another battery and the display, for another $60 you can get an LCD display and a dual voltage controller.