I use my mom's no-name electric bicycle for my daily commute. It is only 3-4 kilometers but there is a big slope. The bicycle's brand and model is Opus E-MOTION, but I cannot find anything online except a picture (see below) and an obsolete shopping listing from French retailer CDiscount (link).
The bicycle used to work wonderfully for a few years now, and I've been commuting with it for almost one year. But since a few weeks, it has a big issue: when the slope is too high, the electric motor stops, and I'm left with a very hard time moving forwards. I think the engine even slows down the bike, I can barely go ahead.
To counter this problem, I move to a flat location as soon as I can, and then I restart the motor again and again, until finally the engine starts again. But it often stops again a few minutes later. Note: I noticed that when I power up the bicycle, the display says "Err 25: maint."
My parents brought the bike to a bicycle tech in my town. He changed the brake pads and adjusted the chain, and said the motor was in good condition.
I tried looking up the brand, the error, and things to do to "fix" an electric bicycle. I also tried commuting with different battery levels - when the battery is full, I can go farther before the engine stops, but it will still stop.
Has anyone had the same issue with no-name electric bicycles? What can I do to fix this?