Why is My Bike Battery Losing Capacity? Challenge Question.

Are you sure you are getting full charge?

Are you sure it is a problem with the battery or other parts causing higher power consumption? Motor, brakes, bearings, has your diet slipped?

Unless you put on considerable weight lately Andy, rapid battery performance deterioration is usually explained by one or two cells inside going belly up. The reason was probably overdischarging followed by one or more cells polarity reversing due to imbalance, age, defect (in that order). Most batt chemistry types as you know are totally wrecked by such a condition. Now if you can dismantle the thing, do it when battery is mostly discharged. Measuring EACH cell voltage both unloaded and with some current load will reveal the dead one(s), and if for example all the others are in decent condition, you could try changing only that. Just don't underestimate 36V, you can get a finger burn by a short or a nasty shock with wet hands. Now 10Ah is not much of a capacity and it wouldn't be all that expensive to change them all, looks like they served you well, they deserve to rest in piece. S.M.

I am thinking it is also a faulty cell.

Some people have had luck reviving a bad cell by overcharging the battery for a short period of time, followed by a regular full charge.

The other possible issue is the battery pack developing a memory and not fully charging. You can try repeatedly fully draining the battery back and recharging to recover the full charge capability.

Batteries do deteriorate, so any revival will be eventually followed by a decline in performance. At some point you just have to bite the bullet and buy a new one or start pedaling more.

It all depends on battery specifics, so I'll wait for more info, but in general all these methods of battery "reforming" are overestimated. In lead batteries for example you can dissolve some sulfuration by cycling and overcharging, but only a small fraction of the released lead stays on the plates, it mostly ends-up as lead sludge in the bottom of the battery, and if plates are high enough and is possible to add lost water, the battery will work with lower capacity. If not, you just create another self-discharging path. And the phenomenon gets worse with spongy (in order to increase metal surface) plates of high capacity batteries. Ni-MH on the other hand, contrary to general belief is less tolerant to over-discharging. It loses capacity permanently and self discharge worsens rapidly. That makes a high voltage (many in series) Ni-MH chain, without provision for occasional balancing, a recipe for disaster, and I don't think one would connect 30 batteries in series to make 36V with no balancing circuit. But then... I've not seen 'em all.(LOL). The same applies for Lithium based batteries, but this pack 5 years ago would have been expensive and Andy would have mentioned the 15+ pin necessary balancing connector and from that figure out that it's Lithium involved. Don't think so. OK now. If it's over about 5KG total, it's lead battery. S.M.

Batteries don't live forever, especially if partial discharges/partial recharges don't match recommendations for the specific battery type.

Not so bad - my wife bought a new electric bike 4 years ago, and the battery became a very heavy paper weight by the next year. Of course, it was just past the warranty period.(also NiMH type)

The new battery, which we were told had been improved, has lasted for 3 years so far.

The NiMH type of batteries are not very long on life. My bike lights with those type of batteries all died within 2 years. I think the expected cycle is some where around 1000 discharge/re-charge cycles. I have seen tips to revitalize these on the internet but haven't tried them yet as they sound a bit like ads for supplements to extend a human life. A Li-ion battery is much more durable - I have bikes lights with these that are 6 years old now and still working fine.

As for a "fix". the electric bikes are still powered by pedals as well as the electric motor - do as I do, pedal the thing. (I have a collection of 10 non-motorized bicycles and ride about as far as you each year, and I am not in flat country) The extra weight of the motorized bike (usually 20 pounds more than an average bike) will get you in shape real quick.

I would start by cleaning all electrical connections.

Maybe the bearings are going bad in the motor....or wheels.....or both......or maybe the brake was dragging, or the tires have lost pressure....Maybe the high winds have increased drag....wiring connections could be corroded or loose.....but most probably the battery is going bad....

Clue, you are the first to mention it, but which one was it?

I know. You are reconnecting with your childhood and going up hill both ways in the snow.

Right on, well done......problem solved. Many thanks for playing my stupid game.....

It proved that we all tend to look for the "involved" answer, and it was the simplest answer of all....I am no better than anyone else by the way!!

I was amazed that a loss of only around 17 pounds of pressure had such a dramatic effect on distance traveled....instead of the normal 45 PSI......I need to check the pressures more often than 2 times per year!!!

We all know about it, but are amazed when its true, well I was......

Thanks for all who played, sorry no prizes....

" sorry no prizes..."

The hell you say. I gave him a good answer. ;-)

So on your question: "Why is My Bike Battery Losing Capacity?" we should have assumed that your "Bike Battery is Not Loosing Capacity". Got it right Andy? S.M.

Battery is fine and has been back to its old performance now for well over a week....

When you rely on your legs for power that is something that you notice immediately. Back in the day when I rode a bike regularly I always checked my tire pressure before I set out on a ride. Even a few pounds low, I felt like I was peddling through molasses. With the help of the motor, it is easy to ignore this.

But still, your battery has a limited life span, and one day you will have to face the reality of replacing it.

All true!

But as the air loss is only very gradual, you tend not to notice it till its really bad....

But when the air is replaced, you notice a sudden dramatic improvement!

You mentioned you got caught out a few times with no power. Did this occur as a reduction to nothing in power, or did you notice an electronic cut out below a certain point?

These battery packs are expensive,,,I think they all come with low power cut off's....

Let's hope it was functioning properly. Failure to cut out, or to cut out in time, could certainly result much reduced capacity.

A new battery costs more than I paid for the bike!!

I was simply not getting as far with the "state of charge" as I had been, I would look and see that I had say 20%, enough for the village shops and back, but it wasn't!

I was caught out several times...till I fixed it!!

If it is like my wife's E-bike - they just quit on you pretty much without warning. Oh, her bike has three cheap LED indicators to give an idea that maybe the end is coming when you are down to 1 light, but when it quits, it quits and she has to start pedaling like the other cyclists around her. At that point she is in a world of hurt as her bike weighs 55 pounds, without the 15 pounds of additional gear she has to carry along, versus the heaviest bike I ride with her at 27 pounds.

Possible battery "memory". Did you discharge, completely, the battery (for NiCa is safe)? Possible for NiMH.

Your solution depends on how honest you are. Four years of heavy use is asking a lot from the battery. Once it starts to go bad , it goes down hill fast. (just like us)

If you are honest, you just bit the bullet and bought a new battery pack (maybe a Li-ion battery) an chalked the cost up as expected maintenance like the brakes, tires and chain.

If you were less than honest, you could have done some minimum of cosmetic repairs and sold the bike to some poor sucker before the battery totally crapped out, and then used the money to buy a new bike.

With 60% of the battery capacity remaining, this would be enough that the poor fool would not notice the problem when they gave the bike a test drive.

The worn tires. The lack of rubber at thread area will make them harder to roll.

Worn tires with thinner tread typically roll much easier.

This is often apparent in the fuel efficiency reduction incurred when you get 4 new tires on a vehicle. Thicker rubber takes more energy to deform than thinner rubber.