AGM Battery Useable Capacity?

Question:

Hi Jeff, a quick question regarding the batteries you installed earlier this year. I believe you said the usable range was between 35% and 85% charged or roughly -110Ahr and -500Ahr for the 780Ahr batteries I have. Is this correct?

Answer:

Hi Ernest,

Your numbers are close for AGM batteries.

The top end of the range reflects the fact that under the absorption rate of charge the time to charge the last 15% of battery capacity is time-intensive and unproductive. As such, you are better to stay within bulk charging which is between 85% and 30%.

• The top end of the range, while cruising will (780 AHrs * -15% = -117 AHrs).
• The bottom end of the range should never be below 30% (780 AHr * -70% = -546 AHrs)

Basically your range is -117 AHrs to – 546 AHrs.