Hoping someone can tell me if this is okay before I mess anything up
I have a 12s4p P42a 4200mah battery on board, and i want to run a 12s6p brick pack as well for extra range, using Lishen LR2170LA cells 4000mah cells - both packs are new.
Is this the correct way? Im not super fimilar with running multiple packs but i have friends that have run it this way
Yes, but it’s best to keep them both connected all the time.
This is extremely dangerous to connect.
But yes, that is correct
the packs are the same voltage when you connect them together. (or within 0.1V or so)
Connecting these together when they are at different voltages is very dangerous.
Once you connect those together, cable tie those fake knockoff XT90 connectors together and don’t unplug them.
yes i asked them if this was okay/safe and they said they make sure to keep them both charged up
They’re correct, the fastest way to get them both at the same voltage is to charge each one with the same charger.
Then verify with a multimeter (don’t accidentally short the battery out!) that they both went all the way to 50.4V
They would both be connected 100% of the time via the picture shown, as they each have their own charge ports
I have used two charge ports simultaneously and others have successfully as well. I’m not going so far as to say this is “safe 100% of the time” as there are a lot of variables.
But I would feel comfortable plugging in two lower-powered, high-quality chargers at the same time.
The rule of thumb here is “charge together, discharge together”
Ask the vendor if they have real Amass branded XT90 connectors.
I’ll change to those ,just used this connector as a point of reference
so its like running a 12s10p? Its just grabbing the same amount of juice from each battery pack?
Just trying to imagine how this thing performs - so it’ll just decrease the time that my 12s4p pack drains? the 4p is the pack that my stormcore reads to my ride-tracking apps
and even tho they are different cells I guess they are very similar in capacity so they should be no problems?
“Should” is a great word but one we really can’t use here. 
But taking all the necessary precautions, and keeping an eye on things as the packs age, can help to prevent any safety issues from popping up.
Capacity differences are really just a performance concern, not an inherent safety issue. The lowest capacity p-group determines the performance (range) for the entire pack.
I don’t think this is even possible unless the multimeter is internally fked. I’m trying to think of how you could do it with a working multimeter and by only connecting the probes to the battery and I can’t think of any way that could happen even if you wanted to short the battery with it. The probe tips are too small and if you can touch both terminals of your pack with one probe then your pack would have already fried itself. the distance is short enough that the current could arc through the air
Well you could either have it on current measuring mode, instead of resistance measuring mode, or, the more likely option IMHO, is you could accidentally touch the two probes together (to each other) while they are stuck inside the female XT connector.
Either of which will probably give you a very, very sharp reminder on how extremely important it is not to do this.
@Crate I would recommend not connecting these in parallel. If you want the jump pack, I would treat is as a second pack and set up some kind of switching system with loopkeys or other, to change between main pack and jump pack.
Keeping everything separate for charging and discharging is just simpler and safer IMO. I think @dskate did something with switchable packs on one of his builds. Spruce moose?
I did. I had two 10S3P packs inside a wooden enclosure on the deck. I wired it so I could swap a loop key from one port to another on the enclosure and switch between the batteries. Worked great. Here is the diagram for how it was wired. I ended up putting a few of the elements in different locations (lcd battery screens, didnt end up doing the underglow etc) but the wiring followed the layout shown here.
And here is the board in action… You can see the loop key ports in the front of the enclosure right behind the front wheels.
This is not a safe recommendation. Charging then becomes a risk. Charge protections on the secondary pack goes out the window.
I really like the dual loopkey input with single key design. As soon as you feel your battery start to sag, you pull out the key and plug it into the other pack. Boom - no sag!
Yeah worked great! I’m considering adding a similar design on my current build so I can do an additional top mount auxiliary pack for longer rides. Then be able to not have it when I don’t need the extra range.
