I have several BB Battery BP4.5-6 Batteries that I want to charge (these are 6V batteries).

To do so, I connected three of them in series. Then, I connect the positive end to the positive output of a V-Infinity (Model EPS180033) 18V 0.33A power supply, and the negative end to the negative end of that same power supply.

At some point over the night, the power supply quits working (I have done this a couple of times, replacing the supply each time) and will no longer put out any voltage whatsoever.

Is this a totally illegitimate way to charge lead-acid batteries?


  • \$\begingroup\$ At some point over the night, the power supply quits working - Are you sure it is not happening right away upon the connection? It would be the most logical scenario.. \$\endgroup\$ – Eugene Sh. Jun 28 '16 at 19:42
  • \$\begingroup\$ I'm quite sure. I unplugged the batteries and confirmed that the supply was still putting out voltage after I first plugged it in. \$\endgroup\$ – user115277 Jun 28 '16 at 19:43
  • \$\begingroup\$ Opening the supply now, it appears that a little transistor inside of the supply exploded (its plastic casing is cracked). I am wondering if my charging method is just completely wrong? \$\endgroup\$ – user115277 Jun 28 '16 at 19:45
  • 2
    \$\begingroup\$ Well. You have fried several PSs, obviously it is wrong :) \$\endgroup\$ – Eugene Sh. Jun 28 '16 at 19:46
  • \$\begingroup\$ Fair enough, but is there anything obviously wrong with just applying a constant voltage to the terminals of the batteries? My next move might be to use a nicer variable output supply on our electronics bench, and I'd prefer not to do that. (i.e. should I be putting a resistor into the circuit to manually limit the current? I would have thought the supply would just refuse to put out any more current). \$\endgroup\$ – user115277 Jun 28 '16 at 19:53

These batteries have a maximum charge current of 1.35 A and your power supply has a maximum rating of 0.33 A. Basically you are running the power supply at it's rated maximum for long periods of time. The fact that it eventually dies is probably because it overheats.

Maximum ratings, can mean, it "can run at this current for ever", or it can mean, "will run for short periods of time at that current but don't do so for longer periods".

I think you've proven the later.

  • \$\begingroup\$ Fair enough. I'll give it another shot with a beefier supply... \$\endgroup\$ – user115277 Jun 28 '16 at 20:10

If you only have 8 volts across three series-connected 6 volt batteries, either they are VERY dead, or you have one battery connected backwards.

Unless the three batteries are known to be in the same state of (dis)charge, you SHOULD NOT attempt to charge them in series - instead, connect them in parallel (or one-at-a-time) to a proper 6 volt battery charger.

A 6 volt charger should produce up to ~7 volts to fully charge a 6 volt lead-acid (or gell-cell) battery, and should have current limiting to protect both itself and the battery.

  • \$\begingroup\$ If they are all in the same state (+/-100 mV or so), it should be OK to connect them in series, though, right? For various reasons, it would be quite inconvenient for me to charge them individually... \$\endgroup\$ – user115277 Jun 28 '16 at 20:10

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.