Short answer: Unplug the battery, look at the base of the pack — not the cable — and count the metal contacts inside the socket. Four square pins and five round pins are two different systems that will not interchange, and a separate two-wire plug (XT60 or similar) means the pack feeds the controller through a cable rather than through its cradle. Write down the pin count, the shape and the socket's width, then match the new pack to those three things plus its BMS rating.

Almost every "wrong battery" return starts here. The cells were fine; the plug was not.

Once you have the pin count and socket width, the packs that use each system are listed here: Reention Dorado and EEL batteries, and Hailong down-tube packs.

1. The three-minute identification method

Do this with the battery off the bike and the key removed.

Step	What to look at	What it tells you
1	The socket in the base of the pack (where it meets the cradle)	Whether the pack connects through its mount at all
2	Count the contacts inside that socket	4-pin or 5-pin family
3	Shape of each contact (square blade vs round pin)	Pin count alone is not enough — 4 square ≠ 4 round
4	Any second cable leaving the pack	Two-wire XT60/XT90/bullet = cable-fed, not cradle-fed
5	The socket width and pin spacing with a ruler	The fit dimension nobody prints in the title
6	The label: voltage, Ah or Wh, and BMS amps	The electrical half of the match

If steps 1–3 do not match the replacement exactly, stop. No adapter fixes a different pin geometry safely.

2. The three families you will actually meet

Family	Shape	How it connects	Real example on sale	Typical electrical ceiling
4-pin square	Four flat blades, wired ++-- (two positive, two negative)	Sliding cradle in the frame	JD-HL085, 48V 10.4Ah / 499Wh, 20A BMS, ≤500W	~500W at 48V
5-pin round	Five round pins; two heavy power pins plus smaller charge/switch pins	Sliding cradle, keyed	JD-JB01 48V 14Ah, 30A BMS, 5-pin — and the DCH-009 folding case	~1000–1500W at 48V
Cable plug (XT60 / XT90 / bullets)	Two-wire connector at the end of a lead	Cable runs from pack to controller	High-capacity rear rack pack, 30A BMS, XT60	1000W class at 48–52V

Two warnings that come straight from the listings:

The 4-pin pack is explicitly sold as 4-pin square, not 5-pin round — the manufacturer states that a 5-pin bike will not fit it. That is not marketing caution; the cradles are physically different.
The ++-- arrangement exists to share current across two contacts per polarity. It is not "two spare pins", and it is not a place to move a wire.

> Pinouts are not standardised across brands. Two packs with the same pin count and the same shape can still be wired differently. Match the part number or the seller's photo, never the pin count alone.

3. Pin count is not ampacity — do the division

A connector tells you what physically fits. The BMS tells you what the pack can deliver. Both have to clear your motor.

Amps the motor will ask for = motor watts ÷ pack volts.

Motor	At 36V	At 48V	At 52V
500W	13.9A	10.4A	9.6A
750W	20.8A	15.6A	14.4A
1000W	27.8A	20.8A	19.2A
1500W	41.7A	31.3A	28.8A

Read that against the two real packs:

The 4-pin 20A pack at 48V is comfortable at 500W (10.4A) and marginal at 750W (15.6A). Put it on a 1000W build and you are asking for 20.8A from a 20A BMS — the pack protects itself and the ride cuts out, exactly like a low-voltage fault.
The 5-pin 30A pack covers 1000W (20.8A) with headroom and sits right at the edge of 1500W (31.3A), which is why 1500W-class builds move up to 40–50A hardware.

So the identification has two halves: pin geometry for fit, BMS amps for function. A connector that fits but a BMS that trips is still a failed purchase.

4. Measure, don't guess — the five numbers to record

Before you message any seller, write these down. They take four minutes and settle the order in one reply.

Record	How	Why it matters
Pin count	Count contacts in the base socket	4 vs 5 splits the whole market
Contact shape	Square blade or round pin	Same count, different geometry
Socket width	Ruler across the socket opening	The dimension titles never list
Case length	Ruler along the shell	A pack 10mm too long will not seat
BMS amps	Printed on the label or the listing	Decides whether your motor trips it

For a cradle-mounted pack, add the cradle type (the base stays on the bike — the JD-HL085 is sold as battery-only precisely because you keep your original cradle). For a cable-fed pack, add the plug type and the wire gauge.

5. Four mistakes that cost a return

Mistake	What happens	What to do instead
Assuming "5-pin" is universal	The cradle keys differently; the pack will not seat	Match the seller's socket photo to yours
Using a 4-pin-to-5-pin adapter	Contact area and polarity are unverified; heat and reverse-polarity risk	Buy the pack with the correct base
Judging by the case, not the socket	Identical-looking Hailong shells ship with both 4-pin and 5-pin bases	Photograph the socket, not the label
Buying a bigger pack on a small BMS	The pack cuts out under load or runs hot	Size BMS to motor watts ÷ volts, with margin

Adapters are the expensive version of a wrong guess: they add a connection in the highest-current path on the bike, and nothing about them is certified as a system.

6. What to send a seller for a definitive answer

Send these four items and the answer becomes yes or no, not "probably":

Send this	What it settles
Photo of the base socket, straight on, in focus	Pin count and contact shape — the fit question
Photo of the battery label (voltage, Ah or Wh, BMS amps)	Voltage, capacity and current ceiling
Motor wattage + bike model	Amps the motor will draw (watts ÷ volts)
Ruler across the socket and case length	Whether it physically seats in your frame or cradle

Then check the certification question separately: the pack itself should be UL 2271 compliant. UL 2849 is the standard for the complete e-bike electrical system — a replacement pack bought on its own is a 2271 question, and no connector photo substitutes for that certificate.

FAQ

Q: How do I identify which discharge connector my e-bike battery uses? A: Take the battery off the bike and count the metal contacts in the socket at the base of the pack. Four square blades means the 4-pin square family; five round pins means the 5-pin family; a two-wire plug on a cable (XT60 or similar) means the pack is cable-fed rather than cradle-fed. Record pin count, contact shape and socket width.

Q: Can I use a 4-pin battery on a bike that had a 5-pin battery? A: Not directly. The cradles and keys are different, and the 4-pin pack is sold specifically as "4-pin square, not 5-pin round" by its manufacturer. You would have to change the cradle and verify the wiring — which is a different job from replacing a battery.

Q: Is a 5-pin connector better than a 4-pin? A: Not inherently — it depends on the current the pack is built for. The 5-pin platform in this range runs a 30A BMS and covers 1000W at 48V; the 4-pin platform runs a 20A BMS and is rated for 500W-class motors. The connector follows the electrical design, it does not set it.

Q: What does the ++-- marking on a 4-pin connector mean? A: It means the four contacts are wired as two positive and two negative, so current is shared across two contacts per polarity rather than one. It is a current-capacity measure, not a pair of spare pins.

Q: How do I know the BMS is strong enough for my motor? A: Divide motor watts by pack voltage to get the amps the motor will ask for, then compare with the BMS rating. A 1000W motor on 48V pulls about 20.8A, so a 20A BMS is at its limit and a 30A unit is the correct choice.

Q: My new battery has the same pin count but will not seat. Why? A: Pin layout and keying differ between brands even at the same count, and the socket width varies. Compare the seller's socket photo with yours and measure the socket opening — pin count alone does not guarantee fitment.

Q: Can I cut the connector off and splice my old plug on? A: That moves the highest-current joint on the bike into a hand-made connection with no strain relief or rating, and a mis-wired polarity can destroy the controller. Buy the pack with the correct base or plug instead.

Q: What should I check besides the connector? A: Case length against your frame or cradle, voltage against the controller, BMS amps against the motor, and UL 2271 certification for the pack. UL 2849 covers the whole e-bike electrical system and is a separate question.

Sources and related reading

JD-HL085 48V 10.4Ah 4-pin pack — 4-pin square ++--, 20A BMS, ≤500W, 499Wh, 360×90×115mm, $209.99; the listing states explicitly that a 5-pin bike will not fit
JD-JB01 48V 14Ah 5-pin pack — 5-pin discharge port, 30A BMS, $277.95
Hailong downtube pack with 5-pin base and XT60 port — from $226.99
High-capacity rear rack pack, XT60 — 30A BMS, $359.99
DCH-009 folding pack — 5-pin discharge, 30A BMS, $249.99
Match an E-Bike Battery to Your Motor & Controller — the amps charts behind Section 3
What BMS Should I Look For in an E-Bike Battery? — current-rating method
Safety: UL Solutions battery safety testing and the CPSC Micromobility Information Center

Data note. This answers a question retrieved 9 times in the 30-question AI-visibility batch collected on 2026-10-16 — one of the highest-scoring topics in that batch that the site had not yet covered. The amp figures are motor watts ÷ pack volts, recomputable for any build; the connector descriptions, BMS ratings, dimensions and prices were read from the live product pages on 2026-10-23.