Your batteries are shot! Lead Acid likely & Either 2,3, or 4 X12volt =48 volt bike. Ebike batteries must be Deep Cycle as car battery will die quickly as they are only good for a quick jolt where a deep cycle can take a big charge loss and then be charged again almost immediately, giving a wee bit of cooling time and a quicker charger will shorten battery life and if you take off right after a fast charge the charge will deplete faster.
If you don't maintain and/or abuse your batteries they get rundown and need replacing.
Understand to conserve power and to not let lithium especially go below 10° Celsius if you can help it or their life expectancy diminishes as well as their output.
I think this is what you are referring to- as you can't go as far as you use to and there is no reset button.
You may have lead acid batteries and they are heavy and need constant maintainance and desulfating trickle charge and must be charged and replaced often. LifePo4 and lithium ion is expensive but you get the benifits again if you don't abuse the battery by full throttle all the time and climbing hills slow as that will kill motor and battery maybe- do some peddling to assist the battery life.
Obviously you need battery replacement and awareness of your bike and how to repair it. Goto Endless Sphere and do a bit of studying- it will do you wonders in time helping to solve ebike issues.
There are ways on YouTube to convert dead lead acid batteries with Epsom salts & deionized water after you drain and neutrilize with baking soda.
Ciao, hope it helps.