Snowball

All I remember is that when I connected the BIG PACK, I've disconnected 3 wires from the other. When I connected the SMALL PACK, I've disconnected 2 wires from the other (one was useless).

You followed me in each step. I won't forget.

CONCLUSION Ok, following your suggestion I was able to figure out the obvious. One of the two battery packs has damaged cells. This is what I did: 1. Opened the wheel2. Checked your scheme3, Disconnected the SMALL PACKAGE (the one on the side)4. Recharge the wheel (it took about two hours) to full (green light)5. Turn on the wheel and check on EUC World: 100% and 83,9V6. The BIG PACKAGE was ok7. Disconnet the BIG PACKAGE (the one under the handle)8. Connect the SMALL PACKAGE9. Recharge the wheel (it took about ten minutes) to full (green light)10. Turn on the wheel and check on EUC World: 80% and 79,3V11. The SMALL PACKAGE was damaged12. I disconnected the SMALL PACKAGE and isolated it13. I connected again the BIG PACKAGE14. I closed the wheel Now I will ask to my friend to order (in guarantee) the Small Package in order to change it. Thanks again you guys.

Thanks so much for your time mate. Appreciated. Evenif you told me it is not as hard as it seems, I think I have to do this work with a guy that knows this stuff more than I do (almost nothing) to avoid any big damage to the wheel. One thing I find very interesting from your walkthrough it that if you find that one battery charged to 100% and the other one charges to 70% (so it's the bad one) you cannot go back and connect them again as they were before. So it is a one way road. Having not a spare battery package, doest it mean that I should use just a single package untill I don't get a new one, I charge them both to 100% and then I reconnect them together? Thank

Thanks for your help. Tomorrow I'm going to make two different test: 1. Trying to open the wheel and use the Electric Tester on those cables (in the above image) following the instruction of @houseofjob 2. Do what you suggested me and charging the single pack (yes, they are two) and see which one doens't charge to 100% (*) (*) Concerning this step, would you be so kind to tell me step by step how to proceed not to make a disaster? You mentioned the risk to reconnect packs with different voltages and I'm scared now

EDIT 2 I've completely recharged the wheel and it went up to 85/84%. So no big changes at all.

Thanks so much for adding the picture. Later tomorrow I will be able to get the electric tester and I will make some measurements. So tell me if I got it right. Measuring package one I will get a value. Measuring package two I will get a different value. The package with the lower value is the bad one. Correct? One more thing. I know I'm a pain in the ass. Sometime the fan/s (the one that starts when you turn the wheel on) make/s a very strong noise. Like it is damaged or there's something wrong with it (maybe it is touching something or whatever...). I've opened as you see in the picture just the side with the batteries, but whatching a teardown video I don't see any fan on the sides of MCM5. Where are those? How can I reach them? Thanks, you guys are pure gold. EDIT: 1) While I'm writing this message I'm recharging the wheel (normal charger). I want to be sure that the trick shown on Youtube (to drain and charge a few times the wheel) doens't fix the issue and let the battery go back to 100% 2) Today I went out for a ride (not a fast one). I started my ride with 69% of battery. Rode for about 16 km and came back with 40%. 29% for a 16 km ride?! :/

Thanks for your opinion. Sadly your theory makes sense. I will check just in order to be sure (doing a few cycles) and let you guys know. By the way, is there a tutorial that explain how to put the shell back (I mean the one the goes around the wheel). I'm going crazy fixing it with all that plastic. Last thing: my friend sold me that wheel for a very friendly price (same he paid) just to avoid me to wait for a new wheel. The wheel was almost new. I will try to find a solution with him. We were unlucky

I've found this video that maybe shows how to solve the issue. https://www.youtube.com/watch?v=fQgr_-r2jGM I commented it in order to be sure i got it right. If so I should ride for a while (at least 50% of the charge), charge it again to full (using the classic charger, not the fast one), chech if the number is above 83%, do the same process again untill I reach 100%. It makes sense to me. What about you?

Correct. 84v and 800Wh. So I should misure both battery (the one under the handle and the one on the side, correct?) with the electrical tester? How do you do it? Any tutorial? Thanks.

Thanks mate. Mine is different than yours. My fan keep spinning at the same speed without pauses.

UPDATE I got the original (not fast) charger. Sadly using it I cannot go above 84%. And while is plugged now, the led is green (as it says "ok, it's fully charged). What I could do to isolate the problem? I upload a picture the shows the battery packs.

Thanks for your answer. So looking at the picture, you say that the charger should be ok, correct? I spoke to my friend and later today he's going to give me the classic (not fast) charger. He says he could fix the problem. I don't get how since the problem seems related to batteries (not charger) and as I said before in a short ride early this morning I consumed about the 10% of the remaining charge. Really strange. I will do my best, helped by him I hope, to try to figure out if those packs inside are degraded...

Here we are. https://imgur.com/a/yE2KFeU I think all the info are here. Not for me,I'm not an expert BTW of course MCM5 V2 shows 6 leds (out of 8) like it is really 80% charged. And, one more thing, I think the battery drains too quick. I rode for about a kg and it seems to have 5% less.

Thanks for your quick reply. I cannot tell you about normal charger because I don't have it. I just got the fast charger. Now I will take the charger, take a few pics and post here.