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As a follow-up to this question, I own a GRUNDIG VCP 3930 vacuum cleaner (which uses a 25.2V, 2000mAh Li-ion battery) that has stopped charging properly. I am being told that the battery on this device might be dead. The warranty period has ended, and I'm considering checking the battery's health myself. I have a multimeter and am familiar with using Arduino and Raspberry Pi for various projects. I would prefer to start with the simplest method first, which would likely be the multimeter, before considering more complex solutions with Arduino or Raspberry Pi.

Could you provide me with a step-by-step guide on how to test the battery's health using these tools? I haven't attempted any diagnostics yet and would appreciate detailed advice on proceeding, ensuring safety and accuracy.

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    \$\begingroup\$ It's not really the health of the battery you should be checking, if it does not charge properly. It may be degraded to the point of being damaged, and damaged batteries are dangerous and can catch fire. \$\endgroup\$
    – Justme
    Commented Jan 22 at 15:40
  • \$\begingroup\$ @Justme Is there a safe way to check if the battery is degraded/damaged? \$\endgroup\$
    – Foad
    Commented Jan 22 at 15:44

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To measure capacity using standard equipment, you'll need:

  • A charger for that battery
  • A current meter (A DVM with a current range)
  • A voltmeter (A DVM in the Volt range)
  • A timer, clock, or the like
  • A dummy load (such as resistor) that will result in a discharge over in one hour (Li-ion) or 20 hours (Lead acid)
  • A spreadsheet open on a computer

You'll also need to know the minimum battery voltage.

Procedure:

  • Fully charge the battery
  • Connect the voltmeter across the battery, to display its voltage
  • Connect the current meter and the load in series with each other
  • Connect the load to the negative of the battery
  • Start the timer and immediately connect the current meter to the positive of the battery
  • Once a minute, note the current in the spreadsheet
  • Continue until the battery voltage drops to the minimum voltage for the battery, or the Battery Management System (if present) shuts off the battery
  • Add all the values for the current, and divide by 60 (to convert from A-minute to Ah).
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    \$\begingroup\$ Thank you, Davide, for the straightforward procedure. I'm curious if it's possible to automate this process with an Arduino or Raspberry Pi for continuous data logging to replace manual timing and recording. Do you have any advice or pointers for setting up such an automated system? Or maybe I can buy something off the shelf to measure the health of different rechargeable batteries? \$\endgroup\$
    – Foad
    Commented Jan 23 at 10:06
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    \$\begingroup\$ "possible to automate this process". Yes, but why bother? Just buy a ready-made Li-ion cell tester. Cheap, guaranteed to work, ready tomorrow. \$\endgroup\$
    – Davide Andrea
    Commented Jan 23 at 13:43

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