October 12, 2025Oct 12 My 26v battery is only reading 18v,I'm guessing a detached wire somewhere, has anyone opened one up and repaired, or is it toast.
October 12, 2025Oct 12 Author It's a raleigh dover bike, not sure how old as i bought it second hand, has been working fine but went for a ride yesterday and it dropped from full 3 lights, to 1 flashing light after about 1 mile,it was fully charged 5 lights on battery, now battery lights just flashing.
October 12, 2025Oct 12 It's a raleigh dover bike, not sure how old as i bought it second hand, has been working fine but went for a ride yesterday and it dropped from full 3 lights, to 1 flashing light after about 1 mile,it was fully charged 5 lights on battery, now battery lights just flashing. That can happen with a battery badly out of balance. It happened to one of mine which cut off in a mile and a half once. When I got it back in balance, I rode it about 36 miles and it still had some go left in it. If batteries are left neglected in sheds this can happen. On the other hand, it might just be knackered. You would need to charge it and then measure the voltages of all the cell groups. When I did that on mine, it was showing numbers around 4.1 or 4.2 on most groups, but one was about 3.4. I can't remember what teh exact voltage was on teh low group but it was well down and nearly flat. What was happening was that when I put it on charge, the BMS cut off the charging when the highest group reached about 4.19 volts. So it appeared all good for a long run, but once on teh road, when the very low group got near to 3.2, it was shutting off. The other groups never got to give their power and when charging the low group never got anywhere near to being fully charged. One job of the BMS is to protect all cells against over charging by stopping charge when any group gets to its full charge voltage and another job is to stop output when any group gets near to its low charge limit somewhere around 3.1 volts. These features together can leave you in this situation of having an apparently charged battery that shuts down after a mile or two. I will leave it to others to tell you how to get it back in balance if that is the cause. Edited October 12, 2025Oct 12 by Tony1951
October 12, 2025Oct 12 Panny 26v systems are very old , likely 10 -15 years old. It is commonly a 24v system, just Panny use 3.7v as the nominal cell voltage rather then 3.6v. Is it lion or Lipo ? If a cell issue then it indicates two cell groups have failed. Edited October 12, 2025Oct 12 by Nealh
October 12, 2025Oct 12 Author It is lion, do cells usually die completely, do they ever just need a wire soldering back in place,I had the idea that the voltage gradually dropped rather than completely dying.
October 12, 2025Oct 12 after that amount of time the cells will have degraded used or not my old bosch 400 batt lasted near 8 years b4 it started dropping voltage fast below 60% charge.
October 12, 2025Oct 12 A detached wire is unlikely to do that. Check battery lights with it off the bike so that nothing's interfering, depending on the BMS a voltmeter could be less reliable. The bike's been working so if the lights don't cheer up it's so far out of balance that the balancing's kaput, or more likely the battery's worn out. Neither's worth fixing and at that age it's safest to replace the battery anyway especially with winter coming.
October 12, 2025Oct 12 It is lion, do cells usually die completely, do they ever just need a wire soldering back in place,I had the idea that the voltage gradually dropped rather than completely dying. Broken wires usually result in a completely dead battery with no output, A typical 24V battery runs from 25.2V at max charge down to 18V at minimum charge, and you said you see 18V. One light corresponds to 18V. Recharge is 5 lights, and you were gettingly a few miles at 3 lights. I think you just have a tired out battery, Those lights correlate to the voltage, but as the battery gets older, voltage doesn;t correspond to capacity, WHen new, you might have had half capacity at 3 lights, but now it could be only ten percent, How does it run if the battery is full charged?
October 12, 2025Oct 12 My 26v battery is only reading 18v,I'm guessing a detached wire somewhere, has anyone opened one up and repaired, or is it toast. I'm not sure that you can read the voltage from the battery directly. Where did you measure it? When was the last time the battery worked properly?
October 13, 2025Oct 13 18v is a discharged state as has been mentioned, if it does not charge then balance will be out or a dead cell group. The BMS needs to allow charging , it will only do so if it cannot detect a fault. A probable issue is balance may be out , but from reading #3 it sounds also like the cells are knackered. If it won't charge then likely a cell group is out of balance and below LVC so the BMS will not allow charging to take place. Aging has a big effect on cells and balance issues and if the battery is circa 10 years old then it is for the most part knackered. In cases like this if charging isn't occurring then it requires the battery case opened to try and determine the fault.
October 13, 2025Oct 13 18v is a discharged state as has been mentioned, if it does not charge then balance will be out or a dead cell group. The BMS needs to allow charging , it will only do so if it cannot detect a fault. A probable issue is balance may be out , but from reading #3 it sounds also like the cells are knackered. If it won't charge then likely a cell group is out of balance and below LVC so the BMS will not allow charging to take place. Aging has a big effect on cells and balance issues and if the battery is circa 10 years old then it is for the most part knackered. In cases like this if charging isn't occurring then it requires the battery case opened to try and determine the fault. Not necessarily, that's typical leakage voltage that you measure when the BMS is switched off. Those batteries don't have a 2-wire connection. IIRC, the BMS is switched off when the battery is not connected to these bikes, so it's not possible to get the actual cell-pack voltage by measuring the output terminals. That's why I asked how the 18v was measured.
October 13, 2025Oct 13 Author Thanks for all the replies,i think it looks like new bike time,the battery will not even start charging now,all five lights are flashing if you press the button,there are new batteries on ebay for around £180,but i dont think they are compatible with my black 4 amp charger,google search is only coming up with batteries around £400 for a 24ah battery,i would be happy with a 15 ah battery or less as i dont go far.
October 14, 2025Oct 14 new bike time https://www.facebook.com/share/17KZ76aytS https://www.facebook.com/share/19iSLgrApk/
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