New battery for swifty at656 (Amazon)

[Domm]

Hi, I was wondering if anyone could help? I have a Swifty AT656 ebike (Amazon one) bought second hand at auction just to try my first cheap ebike. So no warranty or anything. Worked fine before winter. Wintered dry in shed (I know cold not great for batteries but thought "mild" SE UK winter temperatures should be ok). Anyway took out of shed and warmed up to 20°C in house and tried to charge but charger light stays green so no draw on it and bike doesn't turn on any more. The charger is this one:

https://amzn.eu/d/j0dBrf5

So I guess the first thing to check is the charger compatible? It fits in the hole ok and seems to be tye correct one to use for the Swifty's 36v battery but I'm just having to assume it's the correct/standard +/- polarity as I can't find that info anywhere. Can anyone help with this? I have a multimeter just don't know how to use it so maybe it can be used to check this somehow?

So if the charger ok (unconfirmed) I'm assuming the battery is bad? I'm not sure how to confirm this either....except that it doesn't charge/put a draw on the charger.

Does anyone know whether I need to find a battery rebuilder to use/repack the same battery case or if there are any "off the shelf" batteries that will fit this bike?

I'm based near Brighton UK but can post in UK (I guess???) if needed?

I really really wouldn't recommend this bike btw. It gets decent reviews and was fine to ride as a cheap first ebike to try but their parts supply and post warranty customer service is non existent!

Many thanks for any help!

P.S. as a side note if I'm getting a new battery would this be a good project to use the opportunity to "soup up" the bike with for eg a 48V battery, new sine wave controller and display or not worth it/too difficult?

 

[saneagle]

The battery has either gone to sleep or it out of balance, and is probably repairable. Do you have the necessary skills to operate a screwdriver and meter?

 

[Domm]

The battery has either gone to sleep or it out of balance, and is probably repairable. Do you have the necessary skills to operate a screwdriver and meter?

Yes I have a multimeter. I don't really understand how to use all of its functions but I can have a go/learn with a little guidance

 

[Nealh]

Likely out of balance .

 

[saneagle]

Yes I have a multimeter. I don't really understand how to use all of its functions but I can have a go/learn with a little guidance

First thing to do is remove the battery and measure the voltage on the two outer output terminals. If you're not sure how to set your meter, show a photo of it.

Next, you have to measure the voltage on the charge socket, which is a bit awkward if you have the 5.5mm jack type. You have to be very careful not to let your probes touch each other, nor touch both contacts at the same time. In the socket is a central pin and a blade running down the side. It can be done if you're careful and have a steady hand. Alternatively, cut a jack off any old charger, leaving a couple of inches of wire on it, separate the wires and strip back a bit of insulation. Wrap the wires around your probes and insert the jack to get the measurement.

 

[Nealh]

I find with the 5.5mm charge jacks it is easier to buy a cheap counter part to plug in and then probe the contacts .
The speaker Green type uses screws contacts to attach wires so one can simply probe the screws.

 

[Domm]

Thanks for the advice so far. I found a video which is hopefully what has happened to my battery:

No need to watch it but just added for completeness. Basically the battery has unbalanced over winter so he checks the cells and some are too low so BMS has shut down charging
But then the guy has some special charger to individually rebalance the cells (he recommends recharging them very slowly at a couple hundred milliamps) and I don't have one......also someone in the comments said it is not safe to do this anyway and that the damaged cells should be replaced?

So I guess I'm asking if I dismantle my battery and diagnose that it's become unbalanced and the BMS is now preventing charging what is the next step? I suppose at least I'd know in case someone tried to sell me a whole new battery when all it needed was some new cells (or rebalancing if that's safe?)

Or is there a way I could rebalance the cells myself?

Is it safe to do so?

What would I need to do/buy?

Or does anyone know who does this near Brighton UK?

 

[Nealh]

One can't know exactly what has occurred without someone opening the battery and carrying out some fault finding , but an unbalanced /low cell group is likely .

One thing you haven't told us yet is the discharge voltage reading as this can give a clue to whether it is BMS related or a balance issue, theactual reading is significant .