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Interesting table from ADVRider. I didn’t know state of charge and resting voltage showed such a linear relationship.
NOCA genius 10 amp charger is on my wish list as it does charge from a really low voltage and I believe will desulfate as well. At 100 bucks it is not cheap but looks to be a charger that can do almost everything.
Look around your house, I guarantee you have several old Wall Worts stuffed in a drawer that will put out 12 Volts at half an amp or more, these things will revive a battery from dead flat to a point where your fancy battery tender knows what its dealing with.