Can Battery Capacity Shift up or down from Actual to Measured?


I am on the water again in Northern Thailand for my usual five months living on my AGM batteries. You did some work on my Hunter 50 while I was in Vancouver. After three weeks on the water my batteries started resisting charge when my Xantrex Link Pro was showing house banks only 90% full. I blame Acceptance rate as voltage was pushing 14.4 volts with smart charger continuously on float charge. My Xantrex was asking me to synchronize even though it was showing some 65 amps still missing from batteries since last full. If I synchronize my 90% is reset as 100%. What happened to my 65 amps still missing? Is my repetitive resetting drops the full benchmark on my batteries and am I getting less and less work out of them? The batteries are one year old. They were on shore power showing full for half of that time. Thanks for enlightening me. - George


Yes George, it's been a long time. Glad to know you are still enjoying your boat.  You battery monitor is continuously estimating battery capacity and over a period of time the exact battery capacity can either drift up or down from actual to measured. Once your batteries are fully charged, you should take the habit of resetting the battery monitor. BTW, you did NOT lose 65 amp-hours. Your battery monitor had drifted by 65 amp-hours. - Jeff