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10-80V battery monitor with a 0-500A range and selectable shielded lead length
Choose the BM21 configuration by installation distance: 1m, 3m, 6m, or 8m shielded-wire options are listed separately. The monitor covers a published 10-80V voltage range, 0-500A current range, and 0.1-9999Ah capacity setting. It is monitoring hardware, not a battery-protection BMS, so confirm the mounting route and the rest of the system before ordering.
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Product details
SELECTION HELP
FIT AND INSTALLATION NOTES
BM21 is ordered against the unit it attaches to, not against a spec table: the connector, the pinout at both ends and the firmware it has to talk to decide whether it works at all. Confirm those three first, because a mismatch in this class shows up as a device that simply does not answer.
Bought for an existing JKBMS installation that needs a display, adapter or module added to it. Within the JKBMS accessories, that is the job this one is sized for.
Ratings for BM21 depend on the selected configuration, so take them from the spec table on this page rather than from the model name.
Decide early whether the finished installation needs Bluetooth, a wired display, a CAN or RS485 link, or a USB service adapter, because that choice often determines which port is free.
Family position
| Model | From, US$ |
|---|---|
EJ-BM16-500A | 80.00 |
| BM21this listing | 67.00 |
BM19 | 62.00 |
EJ 500A Smart Battery Shunt | 60.00 |
V19 Version 7.0 Inch LCD Display Adapter | 59.95 |
4.3 LCD General Display Adapter | 9.98 |
V19 Version 4.3 LCD Display Adapter | 34.98 |
JK-BLMK-5A | 29.98 |
2.5 LCD Power Board Display | 15.98 |
General 3.2 LCD Power Board | 25.98 |
P-LINK-CR | 9.98 |
RS485-CAN | 6.98 |
There is no ratings comparison to make here. 13 JKBMS Accessories listings are stocked, and which one fits is decided by connector, protocol and physical mount rather than by current or capacity, so compare against the unit this attaches to rather than against the nearest price.
Prices across this group run from US$6.98 (RS485-CAN) to US$103.00 (WiFi Remote Monitoring Module), with this listing from US$67.00. Where two entries sit far apart, the gap is the interface or the bundled hardware rather than the quality of the part, so buy to the requirement in front of you.
Model planning
The figures below are the ones that decide whether BM21 Smart Battery Monitor works in a given pack. Read them against the cells and the load before ordering.
System fit checks
Four things worth settling while the order is still changeable, and one worth doing in the right order once the hardware arrives.
Confirm the exact supported battery string range on the product page. Match the continuous current rating to the actual load and protection design. Confirm the required active-balancing current before choosing a model.
For any inverter-connected system, confirm CAN or RS485 requirements, cable wiring, battery limits, master-slave roles, and commissioning settings before shipment.
Reserve space for the listed dimensions: 15 × 15 × 5 cm. Plan the installation around -10 ~ 60℃ operating conditions. Use suitable fusing, cable size, torque, ventilation, insulation, and commissioning checks for the final battery system.
Bring the pack up on local monitoring and confirm the cell readings look sane before connecting anything downstream. Debugging a protocol handshake against a pack that has an unrelated wiring or balance fault costs most of a commissioning day.
Buying notes
Practical points buyers raise before paying: where the product comes from, what documentation to check first, how it ships, and how the price is set.
This catalogue is operated by JKBMS Electronic Technology Co.,Ltd rather than a reseller, so model configuration, documentation, and warranty questions are answered by the manufacturer instead of being referred upstream.
Parameter sets and connector assignments differ between model families and hardware revisions. Download the manual for this exact model and check it against your pack before commissioning rather than relying on a similar model.
JKBMS boards, monitors, displays, and accessories ship free worldwide. Delivery time depends on destination and customs handling rather than on the order value.
Each configuration is priced separately and the total is re-checked on the server at checkout, so the price shown for the selected SKU is the price charged. Larger quantities are quoted separately through a bulk enquiry.
Product FAQ
Choose the BM21 configuration by installation distance: 1m, 3m, 6m, or 8m shielded-wire options are listed separately. The monitor covers a published 10-80V voltage range, 0-500A current range, and 0.1-9999Ah capacity setting. It is monitoring hardware, not a battery-protection BMS, so confirm the mounting route and the rest of the system before ordering.
Take the figures from the spec table on this page and check them against the pack, the load and the space available. Model names are not specific enough to select on.
One selected EJ-BM21 monitor configuration; The shielded-wire length named in the selected option; Standard supplier packing for the selected unit. Not included: Battery-protection BMS, inverter, battery cells, fuse, shunt cabling, or enclosure hardware not named in the option; A second wire length or spare lead unless it appears as a separate quoted line item. Where a configuration option changes the contents, the option selected at checkout is what ships.
BM21 is stocked here as a jkbms accessories listing. JKBMS hardware is built by JKBMS Electronic Technology Co.,Ltd, and BatteryBoxKit is the storefront that holds and ships it, so orders leave from held stock and confirmations come from zhou@jkess.com.
This page lists 4 configurations, and the one selected at checkout is what ships. Order directly from this page; boards, displays, cables and accessories ship free. If the cart also includes a battery kit, that kit's destination-based shipping rule applies, so confirm the destination before paying.
Shipping and return terms apply to this listing and to every configuration shown above.
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