I see the same question being asked by many newcomers here so I would like to shed some VERY BASIC info on batteries used in esk8, notation, configuration, ratings, etc.
Common battery notation you keep seeing or will see is a (XX)s(YY)p battery with (ZZ) cells:
XX is the number of batteries you have in series ( s ) type connection.
YY is the number of batteries you have in parallel ( p ) type connection.
ZZ is the actual battery cell type used. Samsung 30q is by far the most common here. You will also see 18650 mentioned a lot. That is just the physical dimension of the battery cell, nothing to do with chemistry. It’s a battery 18mm wide by 65.0 mm long. Panasonic, Sony, LG, etc all make 18650 cells. Samsung makes them the best per price for our application. They also make other size cells like the 20700. Can you guess what size that is?
When you add batteries in series, it adds to the total voltage available to your system.
ex. 30Q cells are 4.2V fully charged,
Ie. 10s is 42V, 12s is 50.4V, 100s is 420V etc.
When you add them in parallel, it keeps the voltage the same but adds to the capacity (measured in Ah or more commony mAh).
30Q cells are 3 Ah each (or 3000 mAh if you prefer).
Ie. 4p is 12 Ah (12000 mAh), 10p is 30 Ah, etc.
Very very basically, increasing series adds speed, increasing parallel adds range.
Lipos are safe if you maintain them well. If not, they can puff and make fires. A lithium ion battery pack like discussed above can still burst into flames if you wire it wrong or don’t protect it but are generally safer and easier for beginners. They can give slightly more voltage (power) but also sag faster.
Battery Cell Ratings
Yes, voltage and capacity (those mAh numbers) matter very much. Remember the examples above with series vs parallel?
25r cells are 2500 mAh cells and sag faster than 30q
30q cells are 3000 mAh cells - comparative example
40t cells are 4000 mAh cells and sags less than 30q
25r is what many prebuilts use and are fine. They just won’t carry you very long. Most newcomers I see are upgrading their prebuilt batteries with 30q packs.
You can not mix cell types. Also don’t mix cells of different age (how many times they’ve been used/charged - called cycles).
Each cell also has a listed amp draw rating. Mooch does great testing on cells and often finds reliable discharge and capacity ratings.
Example: 30q cells are rated at 15A discharge by Samsung, 20A by Mooch.
Your battery’s tot available amp discharge is your cell type’s individual amp draw times your number of parallel groups.
A 10s5p of 30q cells will have a max battery amp draw of 100A (20A per cell * 5 parallel groups)
Notice a 12s5p will still have the same max battery amp limit. This is where people will use larger cells to have higher available battery discharges without as many p groups. But the cells are also bigger so balance it yourself for your own use.
After the Battery Upgrade
Your motors are dumb devices. They will happily take whatever your battery sends at them even if it melts them into oblivion. This is where your electronic speed controller (ESC) comes in. It sets the limits of amps (and tons of other things) going to your motors using complex maths I won’t get into. As long as your ESC can handle the voltage rating of your new battery, you’re good to go. You will find this in the esc specs.
BMS and Charging
It stands for battery management system (BMS). It is wired to your battery and keeps the charge even across all of your parallel groups so your battery doesn’t get unbalanced and have problems.
You can charge your pack at different rates as long as they match your pack’s voltage. The charger will be rated in amps to let you know how quickly it will charge your pack. Might as well charge as quickly as possible right? Eh not so much. Charging too quickly is bad for cells and will shorten their lifespan. Charging slowly is best for your pack but worst for riding your esk8 around aot.
Here is a conservative charge rate formula that isn’t painfully slow either:
[# of parallel groups] * [cell type mAh rating / 3000]
For a 10s5p 30q pack (30q cells rated at 3000 mAh):
 * [3000/3000] = 5A charge rate.
Again, you can certainly charge faster or slower than that, this is just my personal recommendation.
Do not ever let your battery pack drain below recommended levels! For this reason, many bms and escs have a hard voltage cutoff where your board will cut all acceleration when too low (cutoff end). You see this happening most going up hills as this draws more power. Most escs used here take it a step further and implement a soft cutoff where, instead of throwing you on your face at a low voltage level, it will slow your board down gradually going to that point (cutoff start). Almost like you’re wounded and limping home to your charger. This brings up the next question, what is a safe discharged rating?
10S li-ion conservative (42.0V charge)
cutoff start 35V
cutoff end 32V
10S li-ion aggressive (42.0V charge)
cutoff start 34V
cutoff end 30V
10S li-ion max-range (42.0V charge)
cutoff start 36V
cutoff end 30V
12S LiFePO4 (43.8V charge)
cutoff start 34.5V
cutoff end 33V
credit to @b264 for saving me the typing
Please keep comments to basic-moderate battery related questions. All advanced battery construction questions should be posted in the battery builders club thread and ONLY AFTER READING THE WHOLE THREAD please.
Welcome to esk8!