> I was told last week that these batteries have a "memory"
> and if you frequently recharge without fully discharging
> them they will loose capacity.
That's mostly a myth, and applies to nickel-cadmium cells, not lead-acid.
> Recommendation was to
> discharge it (with a load like a light bulb) - then
> recharge.
Nope, lead-acid cells hate that. According to Hawker's data sheet
http://www.hepi.com/documents/sbs_spec.pdf
discharging below 9.6 volts will "impair the cells ability to accept a
charge".
> Nominal capacity is 26 AH.
> Used a 12v 50W trouble light as load. I make that a 2.9 ohm
> load with initial current draw (at 12v) of 4.2A.
> 26 AH at 4.2A = over 6 hours capacity - right?
Car batteries' Amp-hours are normally rated at a "20 hour" discharge rate.
Capacity drops off noticeably at higher discharge rates. However, the
Hawker document referenced above says 25.8 AH at a 10 hour rate (to 10.8v).
There's also a chart that says a SBS 30 can only supply 4.07 amps for 6
hours.
> I didn't check the no-load volts but with the 50W load it
> showed 12.1V,
That would be enough for me right there, your battery is on it's way out. A
fully charged, healthy battery should supply 12.6v into a light load.
> Recharged overnight on the Battery Tender. With it still
> attached this morning it was showing 13.14V - presumably it
> had been higher when starting to recharge but had settled
> back to this "holding charge" voltage. Right?
Could be, but I'm not familiar with your "Battery Tender". Some of them
never go high enough to put in a full charge. The Hawker document shows
13.62 as the correct 'float' voltage.
> Did I damage the battery by what I did?
Some, perhaps, but I'd say it was already tired.
> Is it still OK? (i.e. is the above story typical?)
> Or is it about to give up in the middle of the next race?
> Anything else I should do?
Sounds like it has a few more races in it, but not many. Depends a lot on
whether you use it to start the car, and how hard the car is to start. And
of course how much your car draws during a race and how long the race is
(there, is that enough caveats ? <g>)
Randall
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