Is my battery bad?

[Handlebars]

My store bought ebike came with a reention LG 48V 17Ah battery. It arrived about 10 days ago. I've noticed that my mileage seemed weak, especially notice it from 100 %. It drops to 88% in a ride of 7km with taking it no more than 20 km/hr and helping, always pedalling, taking it easy on the battery from the starts after stopping.
Today I put a multimeter on it before I charged it and it was 51.1V at 60% charged. At green light and 100% reported charge on the display, it was 54.2V on the meter.
That's not quite OK, is it?
When I did a calculation from 60% at 51.1V it seemed to pan out correctly for full charge and cutoff.
Any commentary is welcome.
Does it sound like a controller misread, or poor battery?

 

[hellsdragon]

On a meter a 48v battery would read over 50 volts as my 72 volt battery ready 83.5 fully charged I have 6 12 volt batteries in my bike each battery reads 13.7 volts fully charged

 

[Handlebars]

I miscalculated. Used 14 cells instead of 13.

Thank you for your input, hellsdragon !

 

[harryS]

Is it an accurate meter? What do you read on the charger?

What limits the max voltage is the battery BMS. It shuts off charging when any of the 13 parallel groups hits 4.2 volts. Then if you leave the charger connected, even though its LED's may show green, the BMS bleeds a little voltage off the groups at 4.2V, allowing the others at lower voltage to catch up to catch up. It wouldn't be unusual for the pack voltage to be off by a few tenths. Current flow out of the charger during this phase is around 100-150ma, if you want to watch it with a meter.

This is why you should do a full 100% charge once in a while to balance the pack. If you a;ways stop at 80%, the pack can get unbalanced.

48V is 13 groups in series. 52V is 14 groups in series. You're looking at 54.6V at full charge.

 

[Handlebars]

I mistakenly calculated on 14 instead of 13. After I posted I realized and edited to show my mistake.
I have been attempting to keep the charge to less than 80% and more than 40% and to fully charge once every so often.
It's a cheapo charger that was included so it doesn't have anything but a charging light. The display I mentioned is the bike's.
Thank you Harry.

I wanted a large battery so that I could mostly preserve the lifespan but have enough if I needed it. 17Ah was the large battery offering so that's what I got.

I had a brainfart after shopping around so much I guess... that I confused 48V 13S with 52V 14S.

That extra information on what the charger does after reaching "full" is also helpful for my better understanding.

 

[Handlebars]

What limits the max voltage is the battery BMS. It shuts off charging when any of the 13 parallel groups hits 4.2 volts. Then if you leave the charger connected, even though its LED's may show green, the BMS bleeds a little voltage off the groups at 4.2V, allowing the others at lower voltage to catch up to catch up. It wouldn't be unusual for the pack voltage to be off by a few tenths. Current flow out of the charger during this phase is around 100-150ma, if you want to watch it with a meter.

This is why you should do a full 100% charge once in a while to balance the pack. If you a;ways stop at 80%, the pack can get unbalanced.

48V is 13 groups in series. 52V is 14 groups in series. You're looking at 54.6V at full charge.

That is what happened. Now when the battery reads full, it is full. Thanks for the explanation of the behavior, Harry.