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[Graemelawrie]

Evening everyone and Merry Xmas.

So I finished for my short holiday and whats the first thing you do - get the bike out!!

Unfortunately it seems that my battery is empty and now my charger will not start.  I have a new EM 5.7 and It has run beautifully all summer.  It has been about 4 weeks since I last used it and I may have left it on doh!

I've checked all connections and everything is sound, but the battery is showing a low voltage 11.7V - it is a 48V machine.  I have tried everything I can think of but not touching it.  I've tried the 48V charger on my sons bike and all is well - starts up straight away.  So it must be the battery.

Anyone got any advice as to how to move forwards. I'd appreciate it.

Thanks,

Graeme

[KrazyEd]

If the other bike is also 48 volt, and, you can get a parallel connection, you might
be able to "wake up" the battery. Old trick with lead acid batteries. Lithium batteries
seem to have a " off switch " which disables their ability to charge once below a
certain level. I have seen videos of people " waking up " long dead cell phone batteries,
but, not sure how successful this would work with a pack. I have a similar issue with
a 48 volt E Bike battery pack. It was only down to 36 volts, and, it won't charge.
I tried another 48 volt pack in parallel with no luck ( yet ). Hopefully, yours will be better.
Merry Christmas

[BenS]

The spec's for an EM 5.7 states that they have a Lipo battery. I'm no expert, but making a parallel connection with two Lipo's of a very different state of charge is generally considered to not be a good idea, because of the rush of current from the higher to lower voltage battery.

With some experience using Lipo batteries on RC vehicles and E-bikes, 11.7v is considered dangerously low for a 12 cell Lipo(I'm guessing that might be what the EM 5.7 has). The recommended range for a Lipo cell is 2.8-4.2v, so assuming your 48v battery is made up of 12 cells, 33.6v would be the lowest.

Do you know if the battery has a BMS(battery monitoring system circuit board), 'cause a BMS is s'posed to prevent a battery made up of multiple cells from draining below recommended voltage levels?

Does the bike have a voltage meter telling you that the battery is 11.7v, or did you measure it with a multi-meter? If, by chance, the battery is made up of a configuration like 4 lots of 3 cells(i.e. 4 x 12v in series = 48v), then hopefully you got the 11.7v from reading just one lot of 3 cells, in which case 11.7v would have each cell at 3.9v, which is close to a full charge of 4.2v.

The guys on https://endless-sphere.com/forums/ might be better suited to help you.
 

[Graemelawrie]

Thanks everyone. Yes it does have a BMS but obviously did not do the trick ;(. its within warranty so I guess that's the next course of action.  Thanks and Happy New Year.

[Graemelawrie]

P.S Yes I used a multimeter The battery is one unit but so many wires going in and out of it I don't want to mess with it.

[BenS]

Yep, that's probably the best thing to do if it's still under warranty, take it back to the shop and get them to sort it out. 4 weeks isn't that long, so I feel that the battery shouldn't be too bad.