This morning, I wired up a pair of old 50w halogen downlighter bulbs to the old Yuasa 36Ah battery, to evaluate how much Ah capacity was really stored in the battery. Admittingly, this won't simulate the real effects of a starter motor which would be affected by high internal resistance within a poor/sulphated battery.
Discharge test no.1:
At start, 12.4+ volts (no load)
After 1 hour: terminal voltage is 11.70v/8A under load. Estimated 8Ah drawn.
After 2 hours: 9.34v. Total estimated 15Ah drawn.
After 3 hours: 6.76v/6A. Total estimated 20Ah drawn.
After 4 hours: 4v/4A. Total estimated 25Ah drawn.
Approaching 5 hours, 2 volts under load at which point I disconnected the lamps. The open circuit voltage measured around 7.8v after about 10 minutes.
25Ah equates to an estimate of 60-70% charge drawn from the battery, which seems consistent with previous estimates of charge level.
I had hoped to test the Ctek charger's stage 1 - disulphation mode, but upon reconnecting the charger, it appears to have gone straight to stage 2 - bulk charging (constant current). I guess the terminal voltage of 7.8v clearly wasn't low enough. The charging voltage had climbed to about 10.5 volts after 5 minutes.
I also observed the Ctek charger got Very hot while charging, perhaps while delivering fully 3.6 Amp charging current. In hindsight, when the charger was attached to the battery in the car, the charger only felt warm to hot.
Update
After 11-12 hours, the Ctek indicated the battery was fully charged (stage 4 - fully charged/pulse maintenance charge mode). The terminal voltage has only fallen from 13.18v to 13.16v in the past hour. ie. it has not fallen below 12.8v within a few minutes to cause the Ctek charger to switch back to charging mode. Discharging the battery seems to have resolved this issue.
The charge level indicator on the top of the Yuasa battery is indicating the battery requires charging. Prior to discharging, the indicator used to report the battery was OK even when there was a low charge level (12.05v) many months ago. I suspect the indicator was previously faulty/unreliable. It may now perhaps be providing a true indication of the current charge level.
Discharge test no.2:
Initial voltage: 12.57v under 8A load. (13.13v no load)
After 1 hour: 11.93v/8A
After 2 hours: 9.39v
Test halted. Open circuit terminal voltage had slowly risen so far to 11.85v after 45 minutes.
Examining the outer case of the Yuasa battery, it is possible to check the acid level. I also observed there appear to be some sort of white deposit sitting at the bottom of each of the six cells viewed through the casing. Varies in height from 1cm to 2cm measured from bottom of case I think it is lead sulphate deposits. I understand if the deposits become too great, it can short out the plates in one or more cells. The battery would then need to be replaced.
Conclusion: Negligible improvement in estimated maximum stored Ah capacity compared to yesterday's test. Best estimate of 70%. The charge level indicator on the battery also shows the battery needs charging.
I've also observed that to read the charge level indicator correctly on the Yuasa battery, you have to be at least a foot or more above/away from the battery and looking directly down onto the lens. If you are too close or looking at the the indicator lens at an angle, you may incorrectly see a feint blue ring surrounding a grey middle ring encircling a red dot and misinterpret it as a fully charged battery. If the battery is sufficiently charged, the blue ring is Very bold in appearance and surrounds a red dot.
Update
The old Yuasa battery had been sitting in the garage for the past two months. I've now noticed the charge indicator now shows the battery is in Good condition.
