The ZKETECH EBC-B20H is a pack-level capacity tester. It runs a real constant-current discharge on an assembled 12 V to 72 V battery at up to 20 A, measures what actually comes out in amp-hours and watt-hours, and plots the whole curve on your PC.
Read this first: there is no charger inside. The B20H is a discharge tester with a charge-monitoring mode. In CHG mode you connect your own charger to the rear posts, and the B20H meters the charge and stops the run when current tapers. Want a full charge-discharge cycle? You need a charger for your pack voltage. Only want a capacity number? You don't.
Why this tester
This is the instrument you reach for when the pack is already built. Cell testers stop at 5 V and bench loads stop at 30 V. The B20H covers the 24 V, 36 V, 48 V and 72 V packs most people are actually buying, building and selling: server rack batteries, e-bike and scooter packs, golf cart banks, RV and off-grid batteries.
- 12–72 V pack coverageCutoff settable from 8.00 V to 88.00 V. Lead-acid, LiFePO₄, Li-ion and LTO at any series count in that window.
- Programmable constant current0.10–20.00 A in 0.01 A steps. Set current, set cutoff, walk away.
- Real capacity, in Ah and WhResolved to 0.001 Ah on small packs and 0.1 Ah past 100 Ah.
- Four-wire measurementSeparate voltage and current channels, so lead and connector drop don't corrupt the reading. At 48 V and 20 A, that's the difference between a measurement and a guess.
- Graphs you can show someoneEB Tester plots voltage and current against time and saves the run. Show a customer the curve, not a claim.
- Charge meteringWith your external charger, stops automatically when charge current falls below your set value.
- Works without a computerFront-panel buttons and LCD. Software adds graphing and logging.
- Runs on US mainsUniversal 100–240 V AC input.
What you can test
| Pack | Full-charge voltage | Discharge test? |
|---|---|---|
| 12 V lead-acid, AGM, golf cart | 12.7–14.8 V | Yes, up to 10 A |
| 12 V LiFePO₄ (4s) | 14.6 V | Yes, up to 10 A |
| 24 V (8s LiFePO₄, 2x12 V lead-acid) | 29.2 V | Yes |
| 36 V (10s Li-ion, e-bike) | 42.0 V | Yes |
| 48 V (16s LiFePO₄, server rack, golf cart) | 54.4–58.4 V | Yes |
| 52 V / 60 V (14s–16s Li-ion) | 58.8–67.2 V | Yes |
| 72 V (20s Li-ion, 24s LiFePO₄) | 84.0–87.6 V | Yes, to the 88 V ceiling |
| Single cell, or anything under 8 V | under 8 V | No: use the EBC-A40L |
| 96 V and above | over 88 V | No, hard ceiling |
Testing loose cells instead of a pack? The B20H starts at 8 V. For single cells see the EBC-A40L (5 V, 40 A). For packs up to 30 V with charging built in, the EBC-A20.
How much current can you actually pull?
On a 12 V pack the maximum discharge is 10 A, not 20 A (per the manual). Above 12 V the full 20 A range is available, within the unit's power limit.
Most capacity tests run below the maximum anyway. A 0.2 C test on a 100 Ah pack is 20 A; on a 280 Ah bank, 20 A is a gentle 0.07 C. The amp-hour figure is just as accurate at lower current; the test just takes longer.
Worked example: a 48 V 100 Ah server rack battery
A rack battery, new or used, claims 100 Ah and 5 kWh. Here's how you find out.
- Charge to full, with your own chargerThe tester stops the run as current tapers. A capacity test only means something if it starts from full.
- Discharge at constant current (DSC)This step gives your capacity in Ah and Wh. About 5 hours on a healthy 100 Ah pack.
- RechargeLeaves the pack in a sensible state instead of sitting empty.
Set your cutoff above the BMS low-voltage disconnect. If the BMS trips first, the test ends early and the number is wrong. On 16s LiFePO₄, 44.8 V keeps the BMS out of it. For 12 V lead-acid use 10.5 V, and expect rated capacity only at the 20-hour rate.
Reading your results
In a constant-current discharge the current trace holds flat while voltage slides down to your cutoff. The run reports capacity in amp-hours and watt-hours.
Watt-hours are the honest number. A 48 V 100 Ah battery sold as 5.12 kWh that delivers 4.1 kWh has told you something specific, and the curve tells you why:
- Sags steeply from the start: high internal resistance, tired cells, or a bad connection.
- Tracks normally, then falls off a cliff early: usually one weak cell dragging the string. A balancing or cell-replacement job, not a dead pack.
- Shape by chemistry: LiFePO₄ holds a long flat plateau then drops sharply; lead-acid slopes steadily the whole way.
Save the run. A dated discharge curve is the difference between "the battery seems weak" and a warranty claim a supplier will act on.
Technical specifications
| Model | EBC-B20H: 12–72 V pack tester, 20 A |
| Power supply | AC 100–240 V |
| Packs supported | 12, 24, 36, 48, 60, 72 V nominal |
| Discharge voltage range | 0.10–89.00 V |
| Cutoff voltage | 8.00–88.00 V in 0.01 V steps |
| Discharge current | 0.10–20.00 A in 0.01 A steps (10 A max on 12 V packs) |
| Charging | External charger required. CHG mode meters the charge and stops when current falls below the set value |
| Accuracy | ±0.5 % on voltage and current |
| Capacity resolution | Under 10 Ah: 0.001 Ah · 10–100 Ah: 0.01 Ah · over 100 Ah: 0.1 Ah |
| Test timer | 0–999 minutes per step; 0 = no limit |
| Connections | Two front aviation sockets for the battery (positive left, negative right); red and black charger posts on the rear |
| Measurement | Four-wire, separate voltage and current channels |
| Display | LCD: mode, voltage, current, elapsed time, capacity, energy |
| PC connection | Dedicated USB-TTL cable for graphing, calibration and firmware updates |
What's in the box
- ZKETECH EBC-B20H tester
- AC power cord
- USB-TTL cable for PC connection
- Test leads with clips
- Printed manual and software download links
Typical uses
- Checking a used e-bike, scooter, golf cart or EV pack before you buy or after a rebuild
- Incoming inspection on 48 V server rack batteries
- Yearly capacity check on an off-grid or backup bank
- Proving out a pack you just built
- Grading used packs for resale, with a curve attached
- Documenting capacity loss for a warranty claim
- Load-testing 12 V and 24 V lead-acid at a controlled current
Connecting to your computer
The tester works fully standalone. The software turns a number into evidence: a saved, dated curve you can send a supplier or show a buyer.
- Install the driver, then the softwareInstall the USB-TTL driver, then EB Tester. Links are in the manual and at zketech.com.
- Windows in S Mode? Leave it firstOtherwise Windows blocks the install. Microsoft Store → search "switch out of S mode" → Get.
- Power on and plug inConnect the included USB adapter between the tester and your PC.
- Connect in the softwareOpen EB Tester → Comm Setting → choose your COM port (usually COM3 to COM9) → Connect. No port listed means the driver didn't install.
Windows only. ZKETECH confirms EB Tester doesn't run on macOS. Mac users can run the tester from the front panel but can't graph or log runs.
Safety and usage notes
- 88 V is the ceiling. Never connect a 96 V or higher pack.
- Never reverse polarity. Make connections before starting the run.
- Leave the BMS connected and set cutoff above its low-voltage disconnect.
- Size your leads for the current. Poor contact at 20 A means heat and a skewed reading.
- Keep the vents clear. Everything you pull from the pack leaves this unit as heat.
- 12 V packs are limited to 10 A. Design limit, not a fault.
- Use the supplied USB-TTL cable. A normal USB cable won't communicate.
- Test in a clear, ventilated, non-flammable area. Don't leave a suspect pack discharging unattended overnight.
Frequently asked questions
Does it charge the battery?
Not on its own; there's no charger inside. In CHG mode you connect your own charger through the tester, and the B20H meters the charge and stops it when current tapers. For discharge and capacity testing, nothing else is needed.
What charger do I need?
Any bench or pack charger that matches your pack voltage and chemistry. If you only want a capacity number, charge the pack however you normally do and use the B20H for the discharge.
Can it test a 96 V or 100 V pack?
No. Measurement tops out at 89 V and cutoff at 88 V. That covers 72 V nominal packs at full charge and nothing higher.
Why is my 12 V battery limited to 10 A?
That's the specified limit for 12 V packs. The full 20 A applies at higher pack voltages.
Can it test a single cell?
No. The lowest cutoff is 8 V. For single cells see the EBC-A40L (5 V, 40 A) or the EBC-A20.
How long does a test take?
Capacity divided by current. A 100 Ah pack at 20 A is about 5 hours; a 280 Ah bank at 20 A is about 14 hours. Set the step timer to 0 so nothing cuts the run short.
Does it work on a Mac?
Not the software; EB Tester is Windows only. Front-panel operation works on its own.
Do I need a computer?
No. Current, cutoff and timer are all set from the front panel, and the LCD shows running capacity. The software adds graphs and saved runs.
Downloads and support
Download the EBC-B20H manual (PDF)
Software: EB Tester and the USB-TTL driver are free from zketech.com; links are in the manual.
System requirements: Windows 7, 8, 10 or 11, a free USB port, and admin rights to install the driver. Not compatible with macOS.