New Battery for my eBike.

Five years ago I bought an electric assist bike.  I got an Emotion bike. One reason I go that bike was that it used a ‘standard’ panasonic drivetrain, I hoped that would mean there would be many third party batteries available when I needed a new one. The battery that came with is was a 26V 10Ah. At the time a got the bike a replacement battery was about £380. Inn the next few year the price of replacement batteries when up not down as I was hoping! Though the standard battery was now 12Ah.

My ebike when new


Controls and battery indicators:
The on handlebar controls allows for three power settings: economy, normal and sport, you can also turn the assistance off, but when you turn it back on you have to free wheel for a second or so to allow it to recalibrate. If you turn it on while pedaling it gives an error. The handlebar control also uses three lights to show the state of the battery, when the battery is nearly empty the last light flashes. On the battery the state is shown with five lights, again when very empty the last light starts to flash. Both these sets of lights are very stable when I light goes out it does not go back on again till the battery has been charged. One the lat light is flashing there is not much range left in the battery, only a few miles. Once the system thinks the battery is nearly empty it turns off the power. This is done to protect the battery and it’s not good news to flatten a lithium based battery.

The claimed range was 20+ miles. The actual range is very dependant on which power setting is used, how hilly and I suspect the weight of the cyclist! My normal way of using the assist when on a longish ride was for downhill and on the flat turn it off or use the economy setting and only use full power for uphill. When the bike was new with those settings I could get over the Hills to Ledbury and back, with probably one light showing but not flashing. I also managed to cycle from University Station Birmingham to Malvern over 40 miles, but a lot of it was down the Birmingham to Worcester canal where I did not use assist on the towpath.



Bike on the Beacon
Another range test was a cycle to the top of the Worcester Beacon. This used about 80%. This was shown by one or two lights remaining on the battery set of lights.

The battery starts to fail

Due to an accident, on my non electric bike, I did not use the E Bike or charge it’s battery for 6+ months.  When I started to use the E bike again I noticed that range had reduced, The bike and battery were now 4 years old. By looking at the amount of power used by the charge to recharge the battery I estimate the it has reduced to about 60% capacity. I also noticed that the range on flashing has actually increased. Also when the battery was half or more empty the power was not quite as smooth.

This does ask the question what the best way to store a lithium based battery. Although not planned the battery was full charges when I had my accident so I just left it. I knew that leaving it flat was a bad idea.  Another feature of the battery is that when it has not been used for a few weeks it turns itself off and can only be restarted by putting it on the charger. This has the disadvantage you can not simply check the battery charge. has an artical This says that storing at 40% charge is ideal but the it’s not much worse if it has more charge in it. With lithium based batteries storing discharge is bad for them. (this also applies to lead acid based batteries).

So I started to look for a replacement battery, most I found on the net were still expensive. but I did find one from, 20Ah for just £300. So I ordered one but there was a 90 day lead time. So given the time I took working out how the battery was, my procrastination and the lead time it took about a year after I started using the bike again till I go the new battery.

The New Battery

PictureThe new and old battery

When the new battery arrived it was obvious that it was fatter and heavier than the original. So that is how they increased the capacity.  It fits on the bike, though sometimes I feel it with my calf, so It’s a fat as it could be.

PictureNew Battery on the bike

My first tests show it does do have the stated capacity but is behaviour is different in two possible connected ways:

  1. The battery status lights are nowhere as stable the number drop when power is being used and increase when power stops being used.  This applies to both the lights on the battery and the lights on the handlebar control,
  2. Once it is down to two lights the power get less and less even. This is a bit like the old battery became after it lost some of its capacity. The new battery seam to  go on and on forever but getting less powerful.

I think this means the battery controllers  (electronics in the battery)  in the old and new are not the same.

Does this mean that the new one has a less sophisticated one and given the “The new battery seam to  go on and on forever but getting less powerful.” does this mean that it does not have the cut out when the battery is low, I am reluctant to test it as running the battery fully flat would not be good for it.

My plan when using it round Malvern is to normally only charge it when when under power it goes off three light. I think this happens when the battery is about half empty. I can do quite a few trips round Malvern when the lights stay at three.  I would always plan to charge it before a long trip.

Update 2020: The battery is still going strong. The actual replacement battery is now no longer available but a very similar one is still available and as I write this is available for shipping the next day.  This price has gone up a bit but most of this is probably due to the drop in the pound after Brexit.

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