Hmm, I was planning on doing something similar with one of my builds. Would you recommend first just draining one pack, then switching to the other pack mid-ride?
My initial logic was that in paralell each cell would see less load, so I’d get a bit more capacity…
Of course no guarantees 
But just for the details - all brand new P42A cells bought at the same time from an Authorized Molicel/NPE US distributor.
Will do! I’ll report the results
Your input is always greatly appreciated
If I may, I think the key for trying a multiple parallel pack setup is to always ensure both packs are at the same voltage when electrically connected. The only time you can do that is at 100%, or don’t ever connect them (swap one for one).
And the more different the packs are from each other - capacity, internal resistance, chemistry, manufacturing, age, cycles, etc etc - the higher the risk
I know. Just wondering if it’s better that each cell sees, say, a 20A burst load for 5 seconds every 10 seconds, or a 10A burst load every 10 seconds, but in the downtime small current leaking from one pack to the other to balance it. Surely it can’t be that bad?
Agreed. Paralleling the packs reduces the per-cell current, increases efficiency, and would result in a bit more riding time.
How much pack-to-pack current flow there was would be determined by the condition of each pack. With identical packs though, of about the same age and number of cycles, I think that current flow wouldn’t be of any concern.
I recommend monitoring it though as we have no guarantees.
i’ve had a 12s3p where each p was 4.2Ah,
smacced a 12S6Ah pack on top, was ok
(though these were lipos so all i really had to do was add a P group in the wiring harness, no so much like putting a 12s2 p in parallel wirh a seperate complete 12s3p, though that’s sorta similar?
Well…umm…huh?
ya i’m hust as confused 
in other words, i has 8 6s lipos, 6 of which were 4.2Ah and 2 that were 6Ah
had em in series pairs so it makes 12S
so it’d be
4.2-4.2 ]
4.2-4.2 ] all in parallel in a box
4.2-4.2 ]
and then as a range extender, put in parallel but between the box and the esc instead of being directly in the parallel chain? with the others
6.0-6.0
idk parallel is weird explaining when not dealing with whole brick/complete bog boy pack layouts 
anyways
i had no problems with it, worked just fine
at one point i was tenpted to run lipo with liion but that would likely be a very very big nono cause voltsge curves
this winter break tho, gonna try having an extended range pack in my backpack and see if running a cable down to the box caused any issues (assuming i don’t eat it and catch fire)
I’m doing it, two hoverboard packs parallel with my main pack, will get back with how it works as soon as I can finish and test it
What are the configurations of each battery in your setup?
10S5P of VTC6 on the main pack and each hoverboard pack is 10S2P of some 2200 mAh cells
I’ve been skating with external range extender packs for 3 entire seasons now. YES, I’ve had problems, damaged things, so YOU DON’T HAVE TO.
Your main pack needs to be able to handle regen current on it’s own. This means that the pack which can handle heavy charge/discharge current needs to be the main / internal / permanently attached pack.
BOTH packs need their own BMS w/ balancing means.
The charge input of the main pack needs to be rated to handle the max output of the REX pack! This means the BMS of the main pack, and the input jack + wiring harness needs to be able to handle 15-30A. I recommend 16AWG minimum… preferably 14AWG.
The REX pack output MUST run through an “Ideal Diode” circuit. This prevents it from ever drawing juice from the main pack.
You can charge between the 2 packs in the field, but must NEVER charge the REX pack while connected to the main pack. You MUST charge the REX pack while disconnected from the main pack. If you fail to do so, you will very likely dump current from your charger AND the REX pack into your main pack, frying its BMS.
Never connect the REX when it’s sitting at a significantly higher voltage than the main pack! Same reason as above… You’ll dump a ton of current into the main pack very quickly, likely damage/fry it’s BMS.
So long as you avoid these pitfalls, use these tips, whenever you’re cruising, coasting or stopped, your main pack will “sip” from the REX at no more than a few amps.
Why is that? Do you have your REX pack connected to the charge port of your main battery?
Why would the REX pack ever be at a lower voltage than the main one and draw juice?
#nobmsgang
Rusins: I do have my REX connected to the charge port of my main battery now.
Something needs to be able to absorb regen braking current, and if you’re going for capacity, (not ampicity) with the REX pack, chances are it won’t be very happy with 35-40A+ current being pumped into it from braking.
I skated for about 3 months with my latest setup, and occasionally I didn’t have time to fully charge the REX pack before heading out. Especially in this scenario, I ended up field-charging the main pack but not the REX pack. If the REX pack is LOWER, it’s totally safe to connect it (thanks to the ideal diode.) Once the main pack is drained to a lower voltage than the REX, it will begin to draw whatever’s left in the REX pack. I also had the plug connecting the 2 packs get knocked out by a stick once, didn’t notice for miles. I had no choice but to plug it back it if I was to make it to my destination. (This was on what turned out to be a 66mi trek!)
I still discharge directly from the main pack like everybody else. I’ve yet to lay eyes on a hobby/RC charger that handles more than 6S. If you use a pair of 6S Lipo packs + a smart charger / balancer, sure, no need for a BMS on the main pack. BUT, charging without anything to limit charging current near the end of the charge cycle, or to stop the action for cell or pack over-voltage, you’re asking for trouble. Since I insist on a BMS at least for charging, I don’t want heavy current pulled from the REX, I discharge through it. NOTE: In order to make use of the ideal diode, still be able to charge the REX, you either need a BMS with a separate charge port, or to install your charging input upstream of the ideal diode board.
there are plenty that handle up to 8s
source: i have one
i also have put 8k+miles never using a bms 
both lipo and liion
but of course, I always balance charge, by a good balance charger
poastoast… Be that as it may, not everyone came to eskate by way of RC, you get a LOT more bang for your buck in a dedicated 10s or 12s charger. $100 for a 600W charger if you’re prepared to wait, vs similar or more $ for a 200W RC “smart” charger. I’d rather use a $20 30A dedicated 10/12S BMS.
Also, the feedback I’ve gotten from the logs of my smart BMSs has been GOLD. I don’t waste $60+ on that luxury for every battery build, but for a main pack, it is SO nice to see that it’s balancing properly. It also helps speed initial balancing (and to fix an abused pack) when you can force the process to run while NOT charging.
don’t worry, i didn’t start rc til after i started esk8
i do it for travel reasons
This is deceiving to noobs…
…because this is eliminating the need.
I find balance charging with a hobby charger to be a PITA and it completely wrecks most waterproof longboard designs. Specifically, the “waterproof” part. But it will work. It’s a lot easier on a lunchbox emtb.
I just don’t want anyone reading this to think that you don’t need a BMS or balance charging. 
You definitely need one of them.
