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Load testing a house battery bank with a digital load tester — even a $1,300 meter — cannot accurately measure capacity loss in deep-cycle AGM batteries, according to Nigel Calder.▶ 0:14 The only reliable method is a full discharge cycle: fully recharge the bank, discharge it completely, measure the amp-hours out, and compare that figure to the rated capacity.▶ 0:55 Calder acknowledges this is harmful to batteries and should not be done routinely, but it is the only accurate diagnostic when a bank appears to be losing capacity.▶ 1:12 If sulfation is the cause of capacity loss, recovery is possible for flooded and standard AGM batteries — not gel cells.▶ 1:26 AGM batteries with carbon foam negative plates are specifically noted as confusing even high-end load testers.▶ 0:42 The discussion also references a Boat Electrics 101 course covering both capacity testing procedures and sulfated-battery recovery techniques.▶ 1:46

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