John Wayland the inventor of the Insight Shoebox subwoffer and a looong time EV drag racer is generally considered the Insight lead acid (12v) battery guru. And while he dosen't post here (rarely :?: ) here's his oooold post on the topic:
From: John Wayland <
[email protected]>
Date: Sun Jan 26, 2003 6:49pm
Subject: Re: Re: Battery aerobics revisited
Hello hybrid fans,
"josemj1 " wrote:
> --- In
[email protected], John Wayland wrote:
> > ....This is exactly what I've been preaching about when I say that,
> > absent any regular exercise, the Insight's 12V battery will atrophy
> > and loose capacity.
>
> Hmmmm.... The above statement is contrary to all I've read from
> battery manufacturers about lead-acid batteries.
OK, I can do this Hmmmm....thing too
>
> In particular, lead-acid batteries will last for a very long time (>
> 10 years) if always kept topped-off and never discharged below %25 of
> capacity.
If you go back and read 'everything' I've submitted on this, you will indeed, find that my
recommended 'exercise' is this exact routine you've described. Running the 15 amp load of
the headlights for 20 minutes to 1/2 hour (per my recommendation) is a 5-7.5 ahr
discharge....right in line with that 25% of capacity, at 18-28% of the Insight's 12V, 27
ahr battery.
> By topped-off I mean "float-charged" at 13.8V, not
> rapid-charged at 14.4V.
You're a bit off on your description of a float charge. For the typical wet cell or AGM
battery, 13.1V-13.25 is the recommended float level...13.8V is too high for a float level,
and on a wet cell battery you will needlessly gas it, and with an AGM battery, you'll pop
its pressure valves, ultimately destroying the battery.
> The fastest way to kill a (non-deep-discharge)
> lead-acid battery is to discharge it to less than ~6V.
Again, you're a bit off. I set 10.5V as the low limit when under a mild discharge,
certainly not as low as 6V..and it makes no difference if its an SLI type or deep cycle
type (described as deep-discharge), either type is hurt by 6V levels.
> A slower but just as sure way is to put it on a shelf and never float-charge it.
Again, a correction. A high quality AGM type lead acid battery, such as Optima or Hawker,
are far better off 'sitting on a shelf' rather than constantly kept on float. Constant
float without discharges, gradually erodes the positive plate and never allows the battery
to exercise.
>
> I hope that the "regular exercise" you recommend doesn't involve
> frequent discharges below 50% of capacity.
Again, you might want to go back and read 'everything' I've submitted on this. I have
never recommended regular 50% discharges for a non-deep cycle type battery. I do,
recommend discharges in the 18-25% range as opposed to simply allowing the battery to be
on float or in a standby mode without ever having any discharges.
> At any rate, lead-acid batteries don't suffer from the "memory" effect that NiCds are
> suspected of, and so need no "exercise" to restore their capacity.
You are correct about 'no memory effect' for lead acid batteries, but you are wrong about
'no need no "exercise" to restore their capacity'. You might be confusing the two terms
and conditions, they are not the same. Lead acid batteries certainly do need to be
exercised, without it, they lose capacity and atrophy...with it, they stay healthy and can
deliver their full capacity. The fact that so many of the Insight 12V batteries that
rarely get exercised are now at a fraction of their original capacity is a good example of
this.
See Ya.....John Wayland