1. First, determine your bike’s “battery compartment dimensions”—that is, the maximum battery size your electric bike can accommodate. For popular models (such as delivery‑type bikes like the JiuNiu Black Knight), simply provide the model name to the seller; they’ll already know the battery compartment specs. Alternatively, search online for your specific model’s battery compartment measurements, or remove the pedals and rear seat box and use a tape measure to take the length, width, and height. Be sure to check whether the compartment is a regular rectangle or an irregular shape, and share these exact dimensions with the seller to avoid any mistakes.

2. Clearly define your battery’s “core requirements”! Determine the voltage platform of your electric vehicle (48V/60V/72V).

Secondly, range—this is non-negotiable! And remember: for safety, go with lithium iron phosphate. When it comes to pure safety, LFP utterly outclasses NMC and other ternary chemistries. Worried about range plummeting in winter? Keep this old rule of thumb in mind: “NMC in the North, LFP in the South; NMC handles low temps better than high ones.” Ternary batteries do suffer slightly less capacity fade at low temperatures than LFP, but even LFP now offers cold‑weather cells that can charge and discharge normally down to –20°C. Want a battery that lasts longer and has a longer lifespan? Then opt straight for large‑format cells.

3. Hard-headedness: “Battery Cell Grades” On the market, battery cells come in brand‑new Grade A, Grade B, and refurbished (reconditioned) varieties. If your budget allows and you prioritize safety, go for brand‑new Grade A—don’t just trust a seller’s claim that it’s Grade A; don’t place an order based on that alone. Don’t assume Grade A is trouble‑free—there’s a distinction between brand‑new Grade A and refurbished Grade A; make sure you clarify which one you’re getting. Require the seller to provide the specification sheet and test reports for the claimed brand‑new Grade A cells. If they can’t produce these documents, don’t treat it as brand‑new Grade A. As for Grade B, be especially cautious: Grade B cells are often substandard, with issues such as insufficient capacity, cosmetic defects, abnormal K‑values, or elevated internal resistance. If there’s no specification sheet or test report, don’t hesitate to press the seller for clarification. Never assume it’s Grade A. And beware of refurbished cells and second‑hand batteries—especially if you’re new to this. You have no way of knowing how many charge/discharge cycles a refurbished cell has already undergone, nor when it might suddenly fail. Second‑hand batteries are even riskier, with unclear origins and unknown histories. Many so‑called “battery experts” have fallen victim to refurbished cells and used batteries. If you see a second‑hand refurbished cell, steer clear. If price matters more than safety, then consider this advice moot.

4. After-sales: Don’t just take “empty promises”! Make sure it’s backed by a clear guarantee—“X years of warranty, X years of repair.” If the seller can offer free replacement with a brand-new unit for any quality issues, choose them—and they must provide written documentation to back it up.

For battery‑related quality issues, the manufacturer must provide end-to‑to‑end support for the return process. Note: this does not mean simply agreeing to the return; it means assisting with every step of the return procedure. If the manufacturer only agrees to accept the return, you’ll have to arrange for a courier yourself—but couriers often refuse to pick up lithium batteries. You won’t be able to ship them at all! Instead, you must ask the seller to dispatch a courier to collect the battery from your doorstep and cover both the outbound and return shipping costs—this must be confirmed in writing. Additionally, require the seller to provide a written warranty document and an actual physical warranty card; if they cannot provide these, don’t buy.

When buying batteries, never skimp on price or cut corners—do your research, compare options, and prioritize safety, quality, and after-sales service before worrying about the cost. Picking the wrong set of batteries can lead to endless disputes, financial losses, and, in the worst cases, put your life and property at risk.