How to Check an Original Lithium Battery Before You Buy
Knowing how to check an original lithium battery saves you from the most common problem in the market: a nice new case with grade B, used or re-labelled cells inside. This guide explains grade A vs grade B cells, how re-lasered QR codes are spotted, what to look for on the label and in the BMS app, and how to run a simple capacity test at home within the first days of ownership.
Updated 12 November 2026
Grade A vs grade B cells
A LiFePO4 battery is a box of cells (16 cells for a 51.2V battery) plus a BMS. The cells decide most of its life.
- Grade A: new cells that passed the cell maker's full tests, with capacity at or above rating and closely matched internal resistance and voltage. These are what big brands use.
- Grade B: cells that failed some part of grading, such as lower capacity, higher internal resistance or cosmetic defects. They are sold at a discount and age faster.
- Used or recycled cells: taken from old packs, cleaned and sometimes re-marked to look new.
A pack built from mixed or grade B cells may work fine at first and then lose backup quickly, because the weakest cell limits the whole battery.
What a re-lasered QR code means
Large cell makers such as EVE laser-print a QR code and serial number on each cell. Sellers of grade B or used cells sometimes grind off the old code and laser a new one. Warning signs:
- Grinding marks, a dull or uneven patch around the QR code, or a code printed slightly off-square.
- QR codes that do not scan, or scan to a format that does not match the cell maker's style.
- Production dates on cells that are far apart in one pack, or newer than the battery's own label date.
- Different fonts or label colours on cells inside the same pack.
Most buyers cannot open a sealed battery, and opening it usually voids the warranty. Ask the seller for photos of the cells and cell QR codes before sealing, or buy a brand that publishes its cell source.
Check the outside label and paperwork
- Model, nominal voltage (for example 51.2V), capacity in Ah and kWh, and cycle rating should match the datasheet exactly.
- Serial number on the case should match the box and the warranty card.
- The kWh should add up: 51.2V x 100Ah = 5.12 kWh; 51.2V x 314Ah = 16.07 kWh. A "16kW" battery listed with 280Ah cells is really about 14.3 kWh.
- Ask for the warranty terms in writing.
Our product pages show the published specs for each model, so you can compare. Browse all lithium batteries (All Lithium Batteries).
Use the BMS app or inverter display
Many batteries have Bluetooth or a display, or report to the inverter over CAN or RS485. On a new, fully charged battery, look at:
- Cell voltages: all 16 cells should be within a few millivolts of each other at rest. A large spread on a new battery is a bad sign.
- Cycle count: a new battery should show 0 or a very low number.
- Full capacity: should read the rated Ah (for example 100Ah or 314Ah).
- Temperature: all sensors similar, close to room temperature at rest.
If the inverter reads the BMS, see our compatibility guide (Which Lithium Battery Works With My Inverter?).
The home capacity test
This is the most reliable check, and it needs no tools beyond your inverter:
1. Charge the battery to 100% and let it rest for an hour. 2. Run a steady, known load, for example 500W of fans and lights, noting the start time. 3. Let it run until the inverter or BMS cuts off at your normal low cut setting. 4. Multiply watts by hours to get watt-hours delivered.
Compare with the expected figure: kWh x 0.9 x 0.92 x 1000. For a 5.12 kWh battery that is about 4,240 Wh, so at 500W you expect about 8.5 hours. A result far below that, such as 5 to 6 hours, means low real capacity, a high low-cut setting or a measurement error. Do the test within the return or warranty window, and use the backup calculator (Battery Backup Calculator) to get your expected time.
Cell maker codes and 314Ah cells
Most 16kW (314Ah) and 15kW (280Ah) batteries use large prismatic cells from well-known cell makers such as EVE. These cells are popular, which also makes them popular for re-marking. When a seller says the battery has EVE or another brand's cells:
- Ask for photos of the cell tops with the QR codes and the date marks visible.
- Check that all 16 cells look the same and share close production dates.
- Check that the battery's kWh matches the cell size: 16 x 3.2V x 314Ah = about 16 kWh; 16 x 3.2V x 280Ah = about 14.3 kWh.
See all 314Ah batteries (314Ah Lithium Battery).
Other warning signs
- A battery much lighter than the weight on its datasheet.
- A price far below every other seller for the same model and size.
- No serial number, or a serial number that the brand cannot confirm.
- The battery gets hot at modest loads, or swells.
- The seller will not give the warranty in writing.
Buying from a known brand with a published warranty, and testing in the first days, removes most of the risk. See our best lithium battery guide (Best Lithium Battery in Pakistan (2026): Picks by Use Case).
