Can a Mac Portable battery be "trickle charged"?

From: Richard W. Schauer <>
Date: Thu Apr 27 22:35:09 2000

On Thu, 27 Apr 2000, Tony Duell wrote:

> Tell me about it :-). I've never managed to recover a lead-acid battery
> that's been discharged and then left -- there's no 'zapping'-type trick
> that works. If anyone has any ideas on recovery methods, I'd be
> interested to hear them.

I have recovered, at least partially, some small lead-acid gel
cells (small UPS batteries). I've done 3 and one came out like new, one
just good, and one borderline OK. I usually do it over a few days at
work. The basic method is this:

1. Put them across a *current-limited* power supply, set to 2 or 2.5 times
the battery voltage, current-limited to C/10 amps. (that's 1/10 the
amp-hour rating). Initially it will draw negligible current, but since
the voltage is so high it will start to bust through the sulfate and
current will rise. Eventually (a few minutes to a an hour) you'll start
to current limit. When the voltage drops down to near the nominal battery
voltage (perhaps several hours) go to step 2.

2. Take the battery off charge and leave it sit a minute or two. Read
the voltage across it. The lower it reads, the more shorted cells you
have. If it's less than half the nominal, consider giving up. Otherwise
go on to step 3.

3. Charge at C/10 (or even up to C/5) for 2 hours, then put a dead short
across the battery. (I use about a foot-long piece of #16 wire with the
voltmeter across it to see how much current it's putting out. As the
battery improves you will start to pass a LOT of current so be careful.)
The dead short will use the energy in the good cells to blast out the
shorts in the shorted cells. Leave it shorted for 10 or 15 seconds. Put
it back on charge for a few minutes, then take it off for a minute. Read
the voltage again. Repeat step 3 until....

4. When your voltage is up near the nominal battery voltage, and the
battery is able to put out a healthy amount of current (50 to 100 amps
under dead short is not unrealistic), let it charge at C/10 for 10 or 12
hours. Then let it sit overnight or so. If the voltage stays up,
congratulations, you're done. If it drops, try charging at C/10 for a few
more hours until the battery is good and warm. You might still have some
shorted cells and the heat and gassing will circulate the gel a little.

It this doesn't qualify as battery abuse then I don't know what would. :-)
It's a procedure that's technically hard on the battery, but it's already
dead, right? As usual, look out for gassing, excessive heat, and sparks
at the terminals. And if it blows up don't call me :-)

Richard Schauer
Received on Thu Apr 27 2000 - 22:35:09 BST

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