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Mr. Wizard
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Posts: 1042
Registered: 30-3-2003
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Yes that kind of response is normal for a dead as hell battery. The plates are so crystalized with old lead sulfate crystals they don't have much
surface area, and the electrolyte of sulfuric acid is so dilute they have a high internal resistance, and resist current flow. No or little current
flow equals no bulb lighting. Just leave it on for a while. The bulb may never light up to any extent, even if the battery is charging. The bulb is
just there to protect your charger. You may have to charge each battery for a few days to see any result. You will know you have some results when
the battery voltage across the cell starts to drop, as more current flows out of your charger. The charger can only maintain the 15+ volts if it isn't
doing much work (no current flow). Once the battery starts to accept the current the charger will be working harder and the voltage across the battery
will drop as it's internal resistance drops. Multiple charging and discharging and slow rates will sometimes 'reform' a battery if nothing else is
wrong with it.
Once (if) the battery has taken a charge, you can test it by seeing how long it can maintain a .59 amp current ( or any reasonable small fraction of
it's capacity) flow while in the 13.7 (fully charged) to 11.75 (essentially discharged) voltage range. I mentioned .59 amp because that's what your
light bulb will draw. Since your battery is a 4.5 amp hour battery, it should be able to supply a total of time x amps equalling 4.5. Thus drawing .5
amp it should be able to keep it up for 4.5/.5= 9 hours. You can make a chart, and plot amps and voltage over time. You will have to integrate or add
up, the area under the points to get the amp hours. Be advised it will take just as long , or longer to charge it. You would be very lucky if those
two old batteries came close to supplying that kind of capacity. But then you make get lucky ;-)
Keep your eye out for free 'dead' UPS power supplies (Battery Backups) on craigslist. Often the only problem with them is one of the batteries in
them is dead. If you can get a couple of them you can cobble together serviceable set and have a charger as well. They have an excellent charger
inside, and will safely charge and evaluate the batteries. Wires can be brought to the outside of the unit to allow easy connections.
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Oppenheimer
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Posts: 30
Registered: 13-11-2009
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Alright, sounds like a plan. Great info, now I understand that, going back to Ohms Law, V=IR, as the internal resistance in the battery drops the
current flow can increase, and Voltage must change accordingly.
I've had the charger on the battery for probably an hour, it reads @ 12.96-13.13 V WITH THE CHARGER CONNECTED AND ON.
When I turn off the charger and measure just the battery, it reads 10.78V.
I shorted the battery out through the bulb and the bulb lit up nicely, and I put it back on the charger after I realized the battery was holding at
least some charge.
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