One of the reasons that I wanted to join the forum is to get some advice about batteries in general ,and my 48 volt battery in particular . It is a 48 volt battery from Calibike . It is a large and heavy unit , 14 lbs. I cannot remember other specifics about it , and they have discontinued making them . I assume he was making them , but they could have been supplied to him. It is triangular in shape and is held in place with Velcro straps . I have had it for a bit over 3 years , maybe more . My memory is not what it used to be . And I do not keep records . I used it most every day , so I have been guessing that it has had somewhere around 900 or more charging cycles . I believe I have gotten my monies worth . It would seem to do fine fresh from charging , but began to leave me stranded on the return portions of my trips , which were between 20 and 30 miles . It would just go dead . Take it home , charge it up , seemed to take a charge , but then leave me stranded again. I do not have the knowledge or instrumentation to diagnose the problem . And I am under the impression that it can be dangerous to open up lithium batteries . I assumed that I had worn it out . It could be repairable , just don't know . I recently charged it over night and it it took a charge of 45 volts . It has been sitting idle for over a year . I replaced it with a 52 volt unit from Calibike . It is smaller and lighter , but seems to be at least comparable to the earlier battery . More professional packaging , built in mounting on the water bottle mount on most bike frames . It does not seem to have the capacity of the earlier battery . It certainly has fewer cells . What is correct terminology for a batteries capacity ? Is it measured in volts , watts , amperage ? The most notable deficiency is going up a grade .On level ground it is barely noticeable when a battery is half discharged . But on a grade it become very obvious . The hills near my house can start from about 30% slope to around a 45% near the top . A gradual but profound increase. Towards the end of a trip it will barely make to the top . I know that gravity explains the phenomena , but what is is happening in the battery . I figured that all I need is higher volts. But I am slowly coming around to believing that the controller has a large part in all of this . I am the first to admit my ignorance in these matters . Is there a simple explanation , Or should I just buy a book and educate myself . Can anyone recommend a book on these matters ? Electricity for idiot perhaps . Enclosed are pictures of both batteries . Thanks in advance for any suggestions .