My car's battery got flat and the car doesn't start any more. I have a table top PSU rated for 0-15 V, 3.5 A max and 1.7 A continuous, and would like to use it to let the car start again. The battery is a Varta 540 126 034 rated as 12 V, 40 Ah, 340 A. Car is a Honda Jazz from 2006.

I am aware that just connecting the battery to the PSU and letting them go is not a good idea, because that might overcharge the battery and damage it. However, I don't need to carge it fully, just enough so that I can put it back on the car and let it start. Then the car alternator will take care of the rest. Is this feasible without specialized equipment? I have voltmeters and ampmeters.

Specifically, which voltage should I give it? Which max current? How much time to reasonably have enough charge to start the car, yet be sure that I am not damaging the battery or doing anything risky?


At 40 AH capacity that means your 1.5A 15V charger will take 26 hours to provide a 40 AH charge to the battery. You could try hooking it up for 2-3 hours and see if you can get enough charge to start the engine. The 1.5A charge current is going to be nearly "trickle" charge level for an auto battery.

| improve this answer | |
  • It worked. In the end I kept the current a bit lower (between 0.5 and 1 A), because I had rather thin wires. After a couple of hours it was already able to light up the instruments and I probably would have been able to start pushing the car. I charged more or less ten hours in total, and that was enough to start the engine. – Giovanni Mascellani Mar 26 at 11:08

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.