Liitokala Lii-50e Imr 21700 5000mah 3.7v 40a High Capacity Protected Flat Top Rechargeable Li-ion Battery+diy Nicke - Buy Liitokala Lii-50e 21700 5000mah Rechargeable Battery 3.7v 5c Discharge High Power Batteries For High-power Appliances,21700 Battery,21700 5000mah Product on Alibaba.com
with around $3/cell in bulk.
If the 30Ah pack is 6p 14s (typical 52v) that's 6x14 cells, or 84 cells. Let's say they get the cells cheaper in bulk, so it's only $3 each, that's still $252 for the cells...couldn't sell that for only $250. Even if they paid only $2/cell, that's still $168. Let's say they use a garbage BMS for $10, and only another $20 for the interconnects and cell holders and wires, solder, connectors, etc., and use slave labor for building them, so it only costs them $200 in materials to build it (which I think is too low, I expect it actually costs more than they're selling it for, if it were really made of brand new good cells and other quality materials.
BTW, the attached image from their ad claims an explosion-proof enclosure, which it fairly clearly is not. :lol:
And I'd almost bet that hte pics they show aren't even theirs (not an uncommon practice).
Note their "battery size and weight" listing doesnt' actually give the weight, only the outside (?) dimensions.
They only give one set of limits for all versions of the pack, so they probably all use the same BMS, which either means the higher capacity packs are being limited below their actual ability, or the lower capacity packs are being allowed to be pushed beyond their capability.
What the other guys said. With batteries, no free lunch. 52V 14S4P 20Ah Size:310X85X72mm: This size isn't even close.
Pro tip is...take a piece of cardboard and cut it out the size of clearance inside your rider triangle....where current battery resides.
If you need a hand on case shape and size specific to amp-hr, you can pick a common 52V 14S4P Reention or Hailong Shark case and create its silhouette on cardboard, cut it out and see if it will fit in your triangle. Start at 20 amp-hr. 24 amp-hrs starts to get into Jumbo shark cases and many won't fit on common bikes. It wasn't clear to me what bike you have...if its the Yuba Mundo bike you reference which comes with a pretty modest battery. Battery clearance many times is even related to what size frame you ride relative to brand/model.
A typical 52V 14S4P which needs almost 5000 mAh 56cells which aren't inexpensive to create 20 amp-hrs of capacity...borderline decent cells are $5/ea and so just for good A grade cells alone = $280 without case, BMS, nickel strips, fish paper, kapton tape and labor to build it.
Dimensions for this config. case if you want to make a cardboard silhouette are 367mmL X 95mmW X 125mmH.
In batteries, you really get what you pay for.
Let us know if you need more info. As a starting point, consider posting what kind of amp-hrs you think you need, how big the battery you have now is relative to your average ride length etc. Where to buy a good battery is hotly contested. Many will not buy on Ali Express for example for this very reason.
If you want to go for about the biggest Shark case to house qty=70, 21700 cells = 24 amp-hr, below are the dimensions for this jumbo shark case. Its about 30mm taller than a 56 qty 21700 case which is a more universal fit. Depends on the bike.