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I have taken a 10 year old electric bike out of the garage a few weeks ago after not having used it for multiple years. The bike is an elops 7 bought at decathlon with a geonaute battery. It still looks very good and the mechanical parts seem to be working flawlessly (I still plan to take it to a checkout in the upcomings weeks). However I'm having some issues with the electrical parts:

  • When the motor is asking for too much power (when starting or when going up a hill), the control screen and the motor both go off. They can be turned on again but it takes some time and is not a viable solution. When the power needed is low, the motor functions perfectly.
  • The battery seems to lose its power quite quickly, sometimes it's at 3 bars out of 5, and it just goes completeley out of power.

I would like your opinion on the diagnostic and the solution to get it in better shape(and what I've tried so far).

  • It seems to me that there is a problem in the battery (which makes sense because it is old), when talking to a salesman, he said it was very probable for a battery this old.

  • To fix that I would like to change the battery, Decathlon told me the part is not made anymore and that they can't do anything for me. I couldn't find the model on geonaute's website either. The battery is 24V and 10Ah. Upon some research, a battery of this type seems to be around 100-150 euros but wouldn't have the right connectors. Some website also propose battery reconditioning but the price is around 300 euros and it seems very expensive.

Any idea is welcome and feel free to ask for more specific details.

Edit : Added pictures of the battery Battery and battery connector Battery connector

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    Is this the battery the bicycle uses? (in case someone recognizes it from the photos as available under a different name) decathlon.co.uk/p/… – Andrew Morton Oct 21 '20 at 8:31
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    A "HANERIDE E-Bike Pedelec Replacement Battery" looks tantalisingly close. The charge socket is in a different location, and it doesn't have the 4-pin connector at the back, but the power output terminals appear to be the same. – Andrew Morton Oct 21 '20 at 11:27
  • "Geonaute" is/was one of the Decathlon brands. There is no point in looking for a separate company. Decathlon likes to change their brand names from time to time (and re-brand products without changing them), so it is entirely possible that it is available under a different name (as Andrew suggests above). – Szabolcs Oct 21 '20 at 12:58
  • There are many people who will rebuild such battery packs for you. One example here. Many maybes here – Russell McMahon Oct 21 '20 at 23:22
  • According to you, what would be a "good" price to pay for such a rebuild ? – Statistic Dean Oct 22 '20 at 9:55
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As said, the batteries need replacing. They have a limited lifetime, regardless of use. You don't say if they are lead acid or lithium - if lead acid, they will certainly stuffed.

If Lithium they could last many more than 10 years, but only if stored correctly. If replacement batteries cannot be purchased the best option is probably a rebuild. Virtually all battery packs are made up a collection of standard size cells, a rebuild involves stripping the battery and rebuilding with new cells. Cell quality and price varies a lot, so shopping around for the cheapest is not always the way to go, but paying more does not mean you are paying for better quality cells. When selecting a rebuilder, ensure they specify the cells they will be using - ideally a branded named once such as Panasonic or Sony, sourced from a reputable supplier. There are a lot of counterfeit and low quality cells being sold these days.

Changing the connectors to use a different model battery pack is also an option, but you would need to know what you are doing. By the time you source a new battery and installed matching connectors you are likely close the cost of a rebuild.

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  • Regarding the rebuild, the costs I have seen are much higher than the cost of a battery, would you know somewhere where they do it at a reasonable cost with good quality (I live in France). – Statistic Dean Oct 21 '20 at 8:01
  • The question now includes an image with the battery type. – spikey_richie Oct 21 '20 at 10:39
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    Basically a good answer, but I think I would add a warning that batteries can be very dangerous things if you don't know exactly what you're doing. In principle it's not difficult to strip it and it likely contains some standard cells like 18650s that one can replace with some electronics skills, but it's hard to know without seeing it. I agree with your warning about cheap cells, not just that they often don't have the nominal capacity or lose it very quickly, but also can overheat or explode. – Stephan Matthiesen Oct 21 '20 at 13:19
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    You say "rebuilding new cells" but I think you mean "rebuilding the pack with new cells". The cells are sealed cans of chemicals, you don't want to open them, just get new ones. – user253751 Oct 21 '20 at 16:19
  • @StatisticDean questions about shopping are technically off topic, plus you are asking for some specialized expertise and knowledge of France. Unfortunately, you’d be better off investigating this yourself. Maybe start asking e-bike shops, or perhaps even battery repair services for hybrid or electric cars. Battery repair does require specialized tools and experience, plus the person has to know where to buy reliable cells. I think you may just have to put up with the cost. – Weiwen Ng Oct 21 '20 at 16:51
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There are two parts to this question

  1. A 10 year old bike that has been out of use for a while

Check tyres for cracking and flaking. Inflate, and if the tubes don't hold air then replace them (patching tends to be ineffective when the whole tube is old.)

Brake pads also go hard with age - if the brakes are poor then replace them.

Rust - chains and cables could rust-up given the storage. Its often possible to rejuvenate a chain, but a cable that doesn't move well normally needs replacement on inner and possibly outer.

  1. A battery that hasn't been used for 10 years.

Well if the battery can't supply the power needs, then it has lost capacity over time. That it still works at all is amazing - I suspect the battery was charged a couple of times in the decade of storage.

You have four options - replace the whole pack, repack with new cells internally, or hack some other form factor onto your bike. 24V is achievable using two 12V sealed lead-acid batteries, although you'll need a different charger. The bike won't care, though the "power remaining" gauge could be off.

Outside Box thinking Remember you can always leave the dead battery at home and have a rideable bike. It will be heavier due to the motor and wiring, but without a battery at all will be lighter.

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  • The battery has specific connectors, how would you deal with that ? – Statistic Dean Oct 21 '20 at 8:00
  • @StatisticDean Cut the connectors off the bike side as well, and get some other connector you can use. Or solder a short piece of wire to the old connectors, to which you attach the new connectors. (That wire needs to be pretty meaty by the way; at least 1 square mm and ideally better.) – Graham Oct 21 '20 at 9:50
  • @StatisticDean Its a 4 pin connector, and you know its got 24V on one wire, and ground on another. Charge the battery then use a voltmeter into every combination of holes (6 total) to see what the differences are. There may be two wires going TO the battery used for charging - these aren't needed if you have another way to charge the batteries directly. You may need to involve someone with electrical skills at this point - no shame there. – Criggie Oct 21 '20 at 10:21
  • @StatisticDean If the original battery is pretty-much useless now, you could crack it open and explore. Its possible to buy replacement cells, but exactly how they're fitted may vary. Some are spot-welded together, etc, and good ones might have charge balancing/monitoring sensors. You absolutely must use the same chemistry of cell inside, if you intend on using the original charger. It should be okay to fit slightly higher capacity cells, but discharge rates come into it too. If you go this route, try asking on Electronics.SE about repacking a battery pack yourself. – Criggie Oct 21 '20 at 10:30
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    @JeremyBoden for the quoted replacement cost, repacking becomes a reasonable alternative. Or is the bike a throw-away because the battery is no longer available? Planned Obsolescence sucks. – Criggie Oct 21 '20 at 22:03

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