At Luna we get asked this a lot. So here is some info. I have added this to the knowledge base for Fixed for future reference.

Considerations for adding second battery for more range

Generally speaking this is not advisable. It would require extensive modifications and could compromise the battery. Please note that Luna can not take responsibility for the consequences if you break your bike or battery. There are a few separate proposals, we will discuss each below.

Manually switching batteries: Physically unplugging battery 1 from the controller, then plugging battery 2 into the controller. This would be the most straightforward, and eliminates a lot of potential danger in doing the other methods incorrectly. As long as the second battery is a normal 36v nominal battery that should be fine.

Parallel wiring: The idea here being that you would put another battery in parallel. Generally this is strongly discouraged on bms protected packs unless you are unplugging them from eachother when charging, and are making sure both batteries are identical, and both batteries are same voltage at time of connecting them. Given that this would be difficult to meet these requirements there is another way you might go by using a diode to block current from flowing back into the other battery. This page goes over that in more detail. For a working example of this idea in practice, see this page.

Theoretically you could use Luna remote switches on each battery in that parallel circuit, and switch back and forth by turning the one battery off and then turning the other battery on. This would not be advisable due to the possibility of accidentally not turning the other battery off, which would lead to a massive influx of power which could cause a fire. It might be possible to modify a couple remotes to use the same button with a circuit to control making sure that one remote is always off before another one is turned on, but this is outside the scope of what we can advise on.

Charging integrated battery via the charge port: This is unsafe for multiple reasons. Primarily because any second battery you want to wire up will have a discharge rate ten times higher than the safe charge rate on the charge port. This will burn out the charge port instantly and is also likely to damage the integrated battery on the bike. The port expects something like 2-3A, and another battery can put out 20-30A, maybe higher.

Additionally, as with any BMS-protected battery the charge port is how the battery bms is reset if something trips it. So if you are charging the original battery while in use, if something like a short happens in a cell, (which normally the BMS would protect against by shutting down the battery) you may be forcing it to reset despite it not being safe to do so.

In theory you could limit the current of the discharge on the secondary pack using some custom circuitry, so when you plug into the charge port it is not charging it at some massively high rate of current. For example something like this, which can also do CC/CV charging, an important safety consideration. However, you would still be resetting the BMS on the original battery whenever you are charging it. Do so at your own risk.

Links to accessories:

Fenders $37: https://www.amazon.com/gp/product/B00TQ43EXG/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1

Rack $33: https://www.amazon.com/gp/product/B00AA8GFSI/ref=ppx_yo_dt_b_asin_title_o06_s01?ie=UTF8&psc=1

Pannier $55: https://www.amazon.com/gp/product/B07FNP4JZ4/ref=ppx_yo_dt_b_asin_title_o06_s02?ie=UTF8&psc=1

Headlight $68: https://www.amazon.com/gp/product/B01N4ANAPU/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

I just mounted this thing on my front axle:
RockBros Carbon Fiber Bike Kickstand Quick Release Mountain Road Bicycle Stick Stand Black https://www.amazon.com/dp/B06Y5FHLD9/ref=cm_sw_r_cp_api_i_JUqrDb1HQ6VK5

Pros:

It looks cool

It doesn't hang off the bike looking like a kickstand all the time

It stands the bike up when in ideal garage setting

Cons:

It's fragile as hell

Mounting to the front axle makes the bike more unstable than the back would be since the fork can turn

I don't think it will work on a hill

I had to drill out the axle hole to mount it

There are trees, and chairs, and study crap everywhere, I have absolutely no reason that I couldn't just lean the bike against something and have one less part to fool with


But... I guess it looks neat 😉


https://photos.app.goo.gl/De5Kvni2N2vSwqsF9