How to make a 10 year old electric bike battery work better? 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  and battery connector
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.