CTEK MXS 5.0 to rescue dead car battery

hardware
Author

Krasin Georgiev

Published

May 24, 2025

How to recover deeply discharged car battery with CTEK MXS 5.0? The battery has been drained for more than an year and the voltage is below 3V

My experience in recovering a car battery

The question: How to recover 12V car accumulator drained to below 3V?

The case: A new 12V lead-acid car battery (accumulator) has self-discharged to 2.4V. The battery has not been used for more than an year.

Available equipment: CTEK MXS 5.0

Excellent for maintaining and recovering moderately discharged batteries. No manual override — won’t start if battery is very flat (<2V). Great for regular use and keeping healthy batteries in top shape.

CTEK MXS 5.0 battery charger

Initial attempt

So I started charging the battery, following the instructions and selecting “Car” and “Recond” modes.

battery

Unfortunately at normal mode charging stops at stage 5. According to the user manual this means that the battery cannot keep charge.

Charging at step 3 STEP 3 BULK (Charging with maximum current until approximately 80% battery capacity) was very short and at STEP 4 (ABSORPTION, BATTERY READY TO USE) it took about an hour. Than charging stopde at stage 5 (battery cannot keep charge)

The procedure was repeated several times by pressing the red button. No success.

The solution

Charging the regular car battery (50–100Ah) using the CTEK MXS 5.0 in Small Battery mode (motorcycle symbol) actually worked. Charging stopped after 6 hours at Step 2 and the red light was on.

Analysis: Small Battery Mode is designed for smaller batteries — typically 1.2Ah to 14Ah. It uses a lower charging current (0.8A) compared to the normal car mode (5A). As there is a time limit for each charging step and charging a regular car battery (63Ah in this case) at 0.8A will take a very long time, the battery can’t be fully charged if it’s deeply discharged.

The procedure:

  • Charging in Small Battery Mode was repeated several times each with duration about 6h. Finally the charger managed to get through all steps.

  • Charging in Car Battery Mode was started and completed sucessfully after a few more hours

Events:

  • 07.05.2025 09:00 - started at Small battery mode mode

  • 08.05.2025 16:30 - move to Step 3

  • 09.05.2025 20:00 - in Step 7

  • 09.05.2025 20:49 - stopped charging for 50 min

  • 09.05.2025 21:30 - restarted at Car mode, start at Step 4, at 21:50 still in Step 4, 22:30 - in step 6

  • 10.05.2025 04:40 - in step 7

  • 11.05.2025 08:30 - charging stopped