To test the battery voltage all you need is a volt meter, EBike batteries should not ever fall below a certain voltage, google will tell you more about that.. something like 2.2v per cell?? and if they do they may need replacing or reconditioning at best, again beyond my limited experience..
So assuming your battery holds a viable voltage the led indicator on its top and a volt meter will tell you exactly what battery voltage classification you have,
Press the battery test button and if 1 or 2 leds light up and you read circa 40v from the battery Its a 48v battery, But if 3-4 leds light up and its over 40v its a 36v battery
Before you buy any new kit and invest more into a bike you may not be able to ride in daylight (Obvious not within UK regs) and forget about 3rd party liability cover. (nagging over,, honest..) pull all that painters tape off the wires and connect anything thats come untwisted. could be as simple as a shorted out brake sensor, something wired up backwards, or a loose connection..
how many wires connect to each motor btw.. this will indicate if your motors have internal hall effect sensors or not, and is what the 'dual mode' on the controller label relates to I think. the 2 modes being for sensor enabled motors or sensor less motors..
If you have determined whats bad? can you describe how you came to the conclusion?
If you want to try and meet the spirit of the uk regs if not the letter (debate on the impossibility of actually meeting the letter of the regs aside) ie restrict the speed and limit assistance you will need a controller with a display interface. and the KT Ketung? brand mentioned above are popular because of the number of display options (single motor usually) and the range of configurable parameters such as letting you apply throttle only when pedaling etc...
Delivered to the UK even ordered direct from china your looking at £70-100 for a single KT ebike controller and display however.
topBikeKit is a chinese seller recommended on uk forums for spares etc.. inc a wide range of KT controllers
If you need a replacement controller i would simply replace like for like tho aftermarket volt meters are a quid or 2 as are basic speedos that run off a coin cell for years. if you feel the need for either. Tho a speedo is just a distraction on a bike as speed limits dont even apply to cycles or 'legal' ebikes, - not motor vehicles.. (blackbelt barrister - youtube) you judge whats a safe speed while cycling..
btw I didnt mean to knock your bike and perhaps the fact 'LandRover its a model name and not Brand should have been obvious.