Before We Start
This article isn’t meant to be a how-to which is why there won’t be many pictures nor will the pictures go into much detail; this article is meant to be informational only, so if you try to do this mod it’d best to ask someone that has in-depth knowledge about electrical systems.
Using batteries with different voltages and capacities can result in frying the electronics on your bike or worse. Working with batteries can be dangerous and may cause injuries such as burns (both electrical, chemical ), poisoning (from burning battery fumes and fried electronics), and more. You get the picture right?
That’s my warning and I am not responsible if you choose to ignore it 🙂
Let’s Get Started!
Since it looks like a lot of people are liking the 48V mod for the Super73 Z1 I decided to take another look at a dual battery mod on this bike. With a lot of people switching to a 48V setup, something I thought to myself was “What’s going to happen with all the 36V batteries?”
That’s when it hit me to run two stock batteries in parallel in order to achieve more rangw! I had a friend who picked up one of these batteries and when I told him my plan he agreed to let me do the mod on his bike.
Something to note about the Super73 Z1 is the limited range; other than the range this bike is a lot of fun! My friend obtained a stock Z1 battery from someone that did the 48V mod, and his plan was to swap batteries mid-ride. Taking off the seat isn’t difficult, and with enough practice you can do it everything in under 5 minutes, but it just didn’t seem practical enough for me.
Why You Shouldn’t Use Batteries of different capacities
It’s totally okay to run two batteries that have the same voltage even if they don’t have the same capacity. According to battery science (and personal experience), you wouldn’t be able to tap into the extra power of the higher capacity when the smaller battery runs out of juice. This is 99% true but the biggest issue is that the batteries would discharge at rate resulting in a voltage disparity.
Batteries in parallel constantly adjust to each other to maintain an average voltage. When the difference in voltage is high enough, the battery with a higher voltage will send current to the battery with a lower voltage in an attempt to balance things out; this current transfer creates a lot of heat and causes stress (and heat) on the battery discharge cable which is only meant to discharge power (not take it in).
This balancing act is also done on the undamaged side of the Battery Management System whose job is to keep the battery from from being overloaded.
In short to do this mod safely you need to make sure the voltages of the batteries are nearly identical when they are both charged and discharged.
Parts I Used
Stock Super73 Z1 Battery
I chose to use a stock battery because it just seemed easy: I knew it was 36V and I knew the designed capacity was more or less the same as the one in the seat. My friend also bought this 2nd hand battery on the cheap.
This is what would house the 2nd battery. I’ve never been a fan of this bag on my Super73 S1, but it is a tired and true bag and is used a lot people in the community. It was also the perfect size to accommodate the extra battery.
This cable can be used to split one battery into two Anderson connectors which would enable your battery to power the speed controller as well as an additional accessory like a light, or perhaps a USB port for your phone. I chose to use the cable in the opposite orientation so that I could connect the batteries in parallel.
I decided to do a parallel setup because I even though you can just unplug the seat battery and then plug in the 2nd one, this isn’t my style. There are also many benefits range that I will talk about later.
These two connectors were used to add a charging port for the battery using the existing wiring.
Rocker Switch With LED
There is an on/off button in the seat of the Z1 that lights up when pressed and also tells the battery/bms to turn on. I jumped these wires into a rocker switch, because without this switch there’d be no way to charge the battery.
Tools I Used
Although I prefer soldering, this is only version 1 of this mod. I much prefer to solder wires and connectors together, but this was a quick and reliable way to make wired connections
When working with electrical components it’s important to insulate the connections. I used shrink wrap because it looks cleaner and provided additional strength to the wires I connected or joined together.
Electrical tape is just as good of an insulator but can be tricky with thin gauge wires like what come on batteries.
On To The Mod!
The first step in tackling this mod was to create the other end of the charging port so that my friend could use the charger that came with his bike to charge the 2nd battery. Alternatively you can buy a 2nd charger so long as it’s the same spec as the stock Z1.
The XT30 connectors I used came pre-assembled, so all I had to do was strip the bare end of the wires and then screw the wires into the 5.5mm female power connector.
After making the charge port on the 2nd battery I then snipped the 2 pairs of wires going to the switch. I stripped the end of the wires off each and then took the black wire, twisted it together with one of the yellow wires and the crimped on a female spade connector; I repeated the same thing with the remaining red and yellow wires
Next it was a matter of connecting the twisted pairs to the switch and make sure the LED light on the switch turned on.
I was feeling great at this point, so I plugged the charger into the charging port I made, and to my delight the light on the charger went from green to red indicating that the battery was now charging!
I put the battery in the Blackburn bag and then mounted the bag to the bike.
I charged both batteries all the way up and then measured the voltages using a multi meter. At this point I wanted an apples to apples comparison of the range.
The Maiden Voyage
It was my first time riding a Z1 for that long and I was having an absolute blast; I rode along a bike path that follows the San Andreas fault as well as two lakes. I turned on the Strava app to measure my distance and made sure to turn around when I reached 8 miles.
The fun came to an end when the battery went dead; I was able to ride 14.7 miles one one charge. Even though I was a little over a mile away from my car, it did not feel like a walk of shame in any way. I could only think about how happy I was going to make my friend if he could go 25-30 miles. I charged the seat battery back to full after I got home and then plugged the charger into the 2nd battery to double-check and make sure I was good to go for the REAL test.
It was the next day and I picked up my friend so that we could test out the dial battery mod. I showed him how to take off the seat. I connected the single-connector end of the Anderson Y-Cable to the speed controller. Next I connected both batteries to using the Anderson y-cable, and then reinstalled the seat.
Both batteries were switched on, the rear end of the bike was lifter, and then the the throttle was engaged. Success! The rear wheel started turning. I didn’t break the Z1 nor did anything spark or catch fire!
After making sure the connections were seated securely I tucked the power switch and charge port for the 2nd battery into the Blackburn bag. We loaded the bikes and went to the same trail I rode the day previous. I started Strava app on my phone, and then we started riding.
Some of you may be thinking: “Why would you only go 8 miles before turning around if you theoretically doubled the range?” To answer that, it was not because I doubted the mod, but because it was the safer option. This was a practical test in that if we could complete the 16 miles ride it would mean the mod worked (which it did).
We went on the ride and made it back to the car which was a little over 16 miles. The charge light indicator on the throttle stayed green through most of the ride and only dropped to yellow the last 2-3 miles of the ride. Not only that, but the battery didn’t go into overheat/protection like it did on my test ride! The battery had gone into overheat protection mode a few times during my first test.
The battery has over-heat protection that prevents the bike from turning the motor when the battery gets too hot. Heat is the number one killer of batteries and to protect the battery from overheating and potentially melting/burning, the BMS urns off the battery until the BMS is reset or until the battery cools down. This is common if you’re you throttle for a long time or when you’re throttling up a long and steep incline.
The batteries didn’t overheat because the load/heat the batteries were producing were being divided among two batteries. This is not only good for the longevity of the battery, but for the performance as well.
If you’ve ever gone long distances on an eBike, you may have noticed that around 50% battery life the acceleration and speed of the bike decreases a bit. Slower acceleration and lower top speed are all symptoms of your battery getting hot and becoming less efficient. A battery at 50% has to work much harder which generates heat which increases the risk of battery failure and to compensate for that the speed controller may cap the performance in an attempt to lower the battery temps.
In short the batteries stayed at the right temp for the speed controller to say hey we’re not getting too hot so we don’t have to cap the performance!
All together my friend spent around $300 dollars which effectively doubled his range. I think the cost-benefit of this mod is much better than doing a 48V mod (in terms of range).
I mentioned at the beginning that this is version 1 of this mod; the next version of the mod will be to add a digital volt meter since the battery indicator lights are inaccurate and in my opinion useless; I also plan to perform a little nip-tuck on the wires and maybe incorporate the battery switch and charge port into the bag opposed to having them loose in the Blackburn bag.
The 3rd and final version of this mod will include speed-hacking his controller, so that he can go a bit faster. A lot of people have performed the speed hack to their controller to many degrees of success/
Aside from learning more about battery science, but most of all I was happy that I was able to enable my friend because now he’s able to ride longer which opens up the amount of places he can go on his bike!
If you have any questions about this mod comment below, shoot an email to firstname.lastname@example.org, or shoot me a DM on instagram (super73nomad).