DaveB624

It seems that my 36v battery has only 2.75 volts from sitting all winter (my stupidity). Is there any way to bring it back. My charger doesn't touch it.
thanks for any help
Dave

grumpus

A BMS will refuse to charge such a heavily discharged battery, you need to get some volts in there for it to be recognised as a good(?) battery. If you can access the internal connections you can try manually charging each parallel set of cells* with something like a bench PSU - the aim is to get each set over about 2.5 volts, maybe as much as 3.0 V, so you can resume use of the supplied charger. It may be that this process works and you have a working battery (with less life than it had last year) or it may be that some of the cells are so dead you have to open the pack and replace some, or just throw the whole thing in the recycling.


* Risk of serious injury or death: fire and explosion, toxic fumes and corrosive liquid - don't do this without taking appropriate safety precautions.

FBinNY 

Sometimes you can get a slight boost in voltage by warming a weak battery. I'm not saying to put it in the oven, but leaving on a sunny windowsill before connecting it to the charger again. This is kind of a Hail Mary, but at least won't cost anything.

Also, you might do better by asking on the E-bike forum, since that attracts a crowd with more battery experience than you'll find here.

Duragrouch

What about trying an initial charge with a low-amp (like 1 amp) trickle charger, perhaps starting with 12VDC output? If it's not a "maintenance" charger that senses battery voltage, just a simple trickle charger like a typical AC adaptor, it may be able to put some charge in. Low amps is safest I think, don't worry about time. Just in case though, wear safety glasses and have the battery and charger on a fireproof surface or in a metal charging box designed for that.

ScottCommutes

I feel like there is something else going on. A bicycle battery should be able to hold a charge for a few months with no special attention.

Iride01 

You don't offer us any idea what the bike or battery is. And for something drained to that extent, recharging normally might be the next impressive youTube video of a e-bike battery fire.

While the battery should be able to hold a charge for a few months. Many things don't really turn off today and will be a very low but constant drain.

Have you checked with the bikes dealer or manufacturer about what should be done? Anything else and you should make sure you are near by to witness whether something starts going awry. But if the manufacturer or dealer only said to buy another battery, I'd be one of those that tries to revive it first. But probably outside and somewhere fire and fumes won't be an issue.

Welcome to BF

Welcome to BF!

Barry2 

A 36V pack at about 4V per cell is 9 cells. 9 cells at 2.75V is 0.31V per cell. (Edit due to wrong cell voltage)
I don’t think there is any coming back from that.

we are not talking about a voltage level that needs a little help.
Reviving batteries is dangerous, that’s why the manufacturer provided charger has that low voltage cutoff.

I’d never trust that battery pack ever again.
A new battery is cheaper than the deductible on your home insurance.

Barry

FBinNY 

All batteries slowly discharge while idle. If this battery started out with a full charge it should or would have been fine for months.

OTOH if it was put away with half charge or less, then it could bleed down too far, as seems to be the case here.

If the system won't charge it, then it's not meeting the design requirements and for practical purposes is a flammable brick.

Check local requirements for proper disposal.

ScottCommutes

Not an e-biker - my knowledge is more about cars, so perhaps somebody could help me out. Sometimes a car develops a parasitic drain on the battery that slowly bleeds the charge off of a perfectly good battery over time. A classic example is the failure of a switch that leaves one tiny light bulb somewhere on 24/7.

(This can be a bit of a nightmare because the driver may repeatedly try to replace batteries under warranty.)

In this case, if OP has every reason to believe the battery is OK, I would consider checking the bike before it kills the next battery, or at least not storing a battery in this particular bike.

Edit: Break out a multimeter. Put the new battery in the bike and set the bike up like you stored it for the winter. Check for any current flow at all. I would expect there to be stone cold zero - the bike doesn't even have accessories like a clock that a car might have. Measuring amps requires a way to break the circuit and put the meter into the circuit.

Try to get a measurement near the battery so you are checking all possible circuit paths at once.

Iride01 

At least some of the e-bike makers and their battery manufacturers recommend the battery be removed from the bike when it's not going to be used for some time. One even recommends keeping it were it will be between 32° and 68°F. That 68°F would be an issue for my garage in the summer! But that is only talking about when stored and not in regular use.

https://www.aventon.com/blogs/avento...and%2068%C2%BA.

https://www.radpowerbikes.com/blogs/...for-the-winter

https://www.eriksbikeshop.com/blog/p...ic-bike-winter

Barry2 

ScottCommutes ,
With modern electronics (Cars, bikes, TV,) parasitic drain has become a way of life.
Even if all it's doing is waiting to be woken up or maintaining the time on a clock.
Most modern flashlights don't have a true old school battery isolation switch.

It you really want to avoid parasitic drain, isolate/remove the battery.

Barry

FBinNY 

There's a difference between optimal and required conditions. While cool but not frozen might be best, we know there's much more latitude because batteries are shipped globally in all seasons. They have to withstand sitting in a trailer in an Alberta winter, and/or a Dubai summer.

However the shelf discharge rate does vary with temperature, so cooler is better for long term storage, and they MUST be stored with enough charge to not bleed to zero.

ScottCommutes

Choose your poison. If you store them in the house, the batteries will be happier. If you keep them in the garage, there is usually a fire-rated door and a fire-rated wall between the garage and the house to help keep you alive.

The advice about battery storage is the same for all lithium batteries, not just e-bikes.

Even the simple step of disconnecting the battery and leaving it next to the bike is probably a good idea for winter storage.

In other news, my lawn tractor fired right up yesterday after sitting in the shed/yard all winter with zero maintenance. Didn't even need a trickle charge. (gas powered)

FBinNY 

Yep. I store all my emergency stuff with an insulator for the battery pack. Nothing worse than reaching for a flashlight during a blackout and finding the battery's dead.

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Polaris OBark

I have to spray ether (starter fluid) into the intake whenever I try to start mine.

Polaris OBark

I was kind of annoyed that my motor/battery software only lets me run the battery to a 20% charge. This thread makes me realize that is probably a very good idea.

ScottCommutes

Yup. I was guessing something mechanically wrong with a connection that was leaking current. An e-bike battery hopefully has enough juice in it to power a couple of microchips through the off-season.

ScottCommutes

There are a lot of advantages to paying for more amp hours than you need/want/use. As you say, the batteries aren't happy at too low of a charge state. Also, getting a lithium battery to take the last 15% of its charge takes about as much time as getting the battery to take the first 85%. Storing the battery at full charge isn't recommended, either. All of these point to simply getting a bigger battery so you don't have to work it so hard.

ScottCommutes

I use brake fluid to start my generator. I tried it yesterday right after the lawn tractor. It started without the brake fluid for the first time since I've had it.

EDIT: Make that brake cleaner, not brake fluid

grumpus

I suspect you mean brake cleaner, not hydraulic fluid.

Iride01 

Lawn tractor batteries are usually lead acid or similar. Not quite the same beast as a lithium battery.

ScottCommutes

You are correct.

ScottCommutes

You are correct. Regular old lead acid battery.

Bill Kapaun

IF you have a store that specializes in E Bikes, maybe they have some "magic tricks" to revive or know of a place that can "rebuild" the battery for less money than a new battery.

Apparently, a "new" battery for my bike is $750-800? Ouch!

Polaris OBark

How long did you leave it on the charger when you tried to revive it? It might be worth trying for a few days. Do it somewhere safe.