Y cable for 2 batteries
I have bitten the bullet and paid out for the official Y charge lead. It cost me over 200 euros, including delivery, from Outdoor dreams. It took forever to arrive, ordered in early October 2018 and it only arrived last week.
I fitted as per the image on here behind the LHS side panel. Its a tight fit but it just goes in with some careful placing.
There's good and bad news. The good news is I'm able to drive with both batteries connected. Every 15 seconds the battery info is swapped so you get to see the status of both batteries. The percentage remaining charge is displayed of each battery.
The bad news is the range displayed is for each battery so total range needs to be doubled, this is not an issue. What is an issue though is my unit will not allow me to charge both batteries from the bikes charge point. The new unit comes with a lead and a waterproof plug to connect to the bikes waterproof plug under the seat that connects to the charging point. I expected the new unit with the new charging lead connected to the bikes port to charge both batteries but this is not the the case. Reconnecting the original charge plug in doesn't work either. I've tried both my chargers, the original and my new fast charger, ordered from China but not Super Soco, neither is able to charge both batteries simultaneously, they both report battery is fully charged. So I'm currently having to charge each separately, clearly not ideal so I'm in discussion with Outdoor dreams (Frank) to find a solution.
I'll keep you posted on the outcome.
One more point is with the new battery Y lead in place the recharging when going down hill does not work. It maybe related though to the non-charging issue.
I also bought the official Y cable, and I can confirm that I am able to charge both batteries simultaneously, although it takes double the time (or maybe even longer) to charge the two with the standard charger.
I can also confirm that the regeneration function when going down hill no longer works when my y cable is used, so I assume that this is by design, and not a fault. The one advantage, of course, is that the regeneration lag issue doesn't happen anymore.
I hope you get your charging issue sorted, as I have found the Y cable greatly enhances the usability of the bike.