The basic principle behind all battery testers is straightforward: draw energy from a fully charged battery until it is depleted, while logging the total amount of energy drawn.
While there are fully automatic battery testers capable of handling the entire testing cycle—including charging—simple discharge-only testers can be a compelling alternative.
Overview
Discharge-only testers do not have the ability to charge batteries. They depend on you to fully charge the battery before starting the test. Compared to all-in-one testers, they still provide voltage and current logging as well as a test load, but they lack charging functionality.
A Flexible Tool
What may initially seem like a major limitation can actually be an advantage. Having a dedicated battery discharger on hand can be incredibly useful:
- Mass Testing: If you’re testing many individual round cells and want to monitor battery performance, a simple discharger can be an effective part of a streamlined testing setup (see below).
- Storage: Li-ion and LiPo batteries should be discharged to around 3.7V for long-term storage. (LiFePO₄ batteries are an exception, as they tolerate being fully charged for extended periods.) A basic discharger can bring any battery down to a desired storage voltage.
- Safety: When shipping lithium-ion batteries—especially by air—there are both legal and safety recommendations for their state of charge (SoC). A 30% SoC is typically advised for air transport, which corresponds to about 3.6V per cell for most chemistries. A discharger allows you to reliably prepare batteries for safe shipping.
Devices
Here are the common types of battery dischargers:
-
Full-Blown Testers:
Discharge testers like the XH-M239 are designed for testing individual batteries. They feature a built-in load resistor and display key battery metrics. However, such testers often aren’t worth it—for a similar cost, you could invest in a fully automatic tester that includes charging capabilities. -
Discharge Modules:
Compact and versatile modules like the HW-586 offer excellent flexibility. They can be used with any external load resistor, support batteries up to 15V, and allow discharge currents up to 3A. Despite including a display and microcontroller-based monitoring, these modules are remarkably affordable—often available for under €2.00.
Recommended Test Scenario
Most commercially available battery chargers do not include battery capacity testing. This is because they typically lack the ability to discharge batteries.
However, many chargers—even budget-friendly ones—do track the total energy delivered during charging. When you recharge a cell, the charger often displays the total mAh supplied to it.
By combining such a charger with the HW-586 discharger module, you can build a highly flexible and efficient testing setup. Here’s how it works:
-
Battery Use:
Use your rechargeable cells as you normally would.
Once a cell is considered “empty,” you would typically recharge it. However, the voltage at which a cell is considered empty can vary depending on the application. Some devices shut down when the battery voltage drops below 2.8V, while others may cut off at 3.4V—especially under high current draw. -
Discharge to a Defined Cutoff Voltage:
To standardize your testing, place the cells into the HW-586 discharger and discharge them further to a consistent cutoff voltage—e.g., 3.0V. -
Recharge and Measure:
After discharging to the target voltage, insert the cells into your charger. If your charger reports the total energy in mAh, this allows you to evaluate each cell’s actual capacity and track degradation over time—key data for maintaining reliable battery-powered devices.
Slow Website?
This website is very fast, and pages should appear instantly. If this site is slow for you, then your routing may be messed up, and this issue does not only affect done.land, but potentially a few other websites and downloads as well. Here are simple steps to speed up your Internet experience and fix issues with slow websites and downloads..
Comments
Please do leave comments below. I am using utteran.ce, an open-source and ad-free light-weight commenting system.
Here is how your comments are stored
Whenever you leave a comment, a new github issue is created on your behalf.
-
All comments become trackable issues in the Github Issues section, and I (and you) can follow up on them.
-
There is no third-party provider, no disrupting ads, and everything remains transparent inside github.
Github Users Yes, Spammers No
To keep spammers out and comments attributable, all you do is log in using your (free) github account and grant utteranc.es the permission to submit issues on your behalf.
If you don’t have a github account yet, go get yourself one - it’s free and simple.
If for any reason you do not feel comfortable with letting the commenting system submit issues for you, then visit Github Issues directly, i.e. by clicking the red button Submit Issue at the bottom of each page, and submit your issue manually. You control everything.
Discussions
For chit-chat and quick questions, feel free to visit and participate in Discussions. They work much like classic forums or bulletin boards. Just keep in mind: your valued input isn’t equally well trackable there.
(content created Nov 09, 2024 - last updated Apr 23, 2025)