What are the best practices for recharging a 12V lead acid battery with a manual recharger.

I have a 12V lead acid battery (7.2AH/20HR MK ES7-12 (PDF)). I've read the advice here on how to check the battery level (I have ~12.2 V under no stress, and when powering the system it still currently reads ~12.2 V on the DMM).

When it starts to run low, I'd like to know how best to recharge the battery. I have a manual battery charger (Schumacher MC-1). I realize the manual part means that I cannot just plug the battery in and walk away. How best to monitor the charge? With what frequency? What likely problems should I be aware of?


Not many issues charging big lead acids. Just hook the sucker up, turn it on, wait a while, test the battery for either loaded voltage or charge current (<0.3A), then disconnect or continue. Some issues I've had with standard sealed lead acids:

  1. Killing the battery separates the water from solute, which can then freeze. This happens if it dies in the cold. It's basically pooched at this point, but there's nothing stopping you from trying to thaw it out and charge it back up. Sometimes they still work!
  2. Don't use the boost function, if there is one, to attempt to charge the battery more quickly than usual. This is strictly for boosting, and will reduce a battery's MTTF. Note that maximum charge current is 2.16A.
  3. Charge it in a ventilated area. I know it's sealed, but I do this anyway, just in case!
  4. Don't put it on a concrete floor -- stick a piece of cardboard or wood under it. This has been proven a myth a dozen times over, but I still do it to keep Murphy at bay.
  5. Don't use too large a maintenance charge. The battery datasheet states 13.5V-13.8V float voltage.

Why did you get a manual charger, anyway? I'd definitely screw that up within a season.

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  • \$\begingroup\$ What's the story behind concrete floor? \$\endgroup\$ – AndrejaKo Jan 10 '11 at 1:37
  • \$\begingroup\$ @Andrejako, Here's one version. \$\endgroup\$ – tyblu Jan 10 '11 at 3:10
  • \$\begingroup\$ You say, "wait a while, then test". Every 5 minutes? Every 30? Also, do I need to unplug from the charger, plug into the system, load it, and then test? If I over-charge it is a problem after roughly ____ minutes? \$\endgroup\$ – mankoff Jan 11 '11 at 22:07
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    \$\begingroup\$ @mankoff, Wait 'til it's supposed to be done under ideal conditions (1Ah in = 1Ah stored), test then and every 15 minutes thereafter until it's finished. How are you testing it? I use a 30W bulb at work, but make mistakes pretty often due to the variety of brands, ages, and electrolyte concentrations (not the sealed type). \$\endgroup\$ – tyblu Jan 11 '11 at 22:49
  • \$\begingroup\$ I'll test it by hooking it up to the motor it drives and turning the motor on, then checking the V. Also, I got the manual charger because it was cheap and I'm on a budget... Perhaps not worth the savings if it'll be problematic. \$\endgroup\$ – mankoff Jan 11 '11 at 22:57

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