GM Merge Battery will not charge

[Iceman218]

I have two GM Merge eBikes and they both work great. My understanding is the batteries are about 46 volts. I take the batteries out of mine often to stop the bike from draining them. I have an acquaintance with a Merge and the first time the battery came out was two days ago when I went to look at his issue. His bike is 2.5 years old will not charge. I tried his charger on my battery and it worked fine. I tried both my charger and his on his battery, but only got a brief blip of charging before the charger went to standby mode again. When his battery is in the bike, it will turn on and set fault codes for low charge. But in or out of the bike it will no longer charge. With my battery in his bike, it operates fine. Since his battery is not a brick yet, is there a way to jump some voltage into it and get it awake to charge?

 

[ElHegpah]

The voltage is unusual and the chemistry is unknown.

Also, being from GM, good odds there are some unusual protection/replacement prevention strategies in place.

As a general rule, with a standard config, li-ion battery, if the BMS has tripped into a protection mode, then, SOMETIMES briefly charging thru the outputs for a "fairly short" period of time, can reset it.

Both RIGHT NOW, plus during procedure, plus after, store this battery outdoors inside a BBQ.

Removing the battery from the bike does not really solve the self-drain problem. It is the BMS, internal to the battery, which usually causes the problem, ESPECIALLY if the battery has been stored several months without charging. The BMS, sometimes called a Battery Murdering System, drains just a small amount of power, but ONLY thru just one parallel group of cells. Over several months these can become drained past the point of no return, and charging them can become extremely hazardous.

Ideally, each of the individual groups can be tested at the BMS, if none have gone below 2.0-2.5 volts, you should be OK. Iffy below 2.0, if below 1.0 dig a hole and bury it, it is dangerous and non-recoverable.

Unless it is Lithium Titanate. Unlikely but possible.

Edit to add - Looks like parts of this bike, in particular the BMS design, may have come from Bionx designs, if so, Holy Crap, you are so screwed, run away, run away.

 

[Iceman218]

The Charger is from BMZ if that helps any, with a 49.2V output at 1.75 amps. Since the BMS in a hard gel, removing the gel will break wires at a minimum so my probing is limited to the 8 connections that plug into the bike. But that I can do.

 

[ElHegpah]

Standard Li-ion voltage is multiple of 4.2. You have something different. Possibly Lifepo4. It is a safer and more tolerant chemistry, while being a bit heavy and bulky.

You do have a bit of ebike history. This is the bike that put Bionx out of business, it's a long story, but interesting. It's a playbook for how to mismanage a company with lots of ideas, and lots of stupidity.