I have a 500w 48v e 13 amh bike. I suspect the fuse is faulty
 

It will not charge. When this happened before, I took out the fuse, put it back in and it charged fine.

Now it is not charging again. The light on the charger is green and is warm so I assume it is not the charger.

The fuse has no markings on it to determine what it is. The metal filament doesn't look burnt. I am not good at this kind of thing as a retired gal but I am determined to figure out how to do a bit of maintenance on my own as the shop is a long way away. Do I just get a 13 amp fuse? What is a '13 amh', the fuse??)

I'm going to buy a voltmeter because with all this exposed wiring (ebike kit) I think it will be good way to track down what is not getting power.

If you've gone and purchased a multimeter then it should be easy to check the fuse. Remove the fuse, set the meter for resistance, (ohms) and put one lead on either side of the fuse. You should have a very low resistance value and if so, the fuse is good.

If the fuse is good, then you can start looking at voltage beginning at the output of the charger and checking at every connection between there and the battery.

If you can get the wiring diagram of the bike, look it over. Even if you don't have an electrical background, you may learn something that makes it easier to troubleshoot.

While waiting for your fuse/meter, consider if your charge sequence needs to be changed. Some chargers want you to connect into the battery with the AC unplugged. Then when you plug in the power, they will charge. Other chargers will start charging if they are already plugged into the AC first when you connect to the battery. Hope it was as simple as this.

Fuse???
Where did you find this fuse? Is it in the battery compartment? Did you disassemble your battery pack?

Depending on the fuse type they are visual indicators if it is burnt out or not. Is is a wire in a glass tube?
Is is a flattened wire stretched across a ceramic pin? Either will be clearly broken if burned out.
IF it is burned out: you need to fix the cross before you install a new fuse or you will just burn out the new one.