Does the Voltage Drop When My Batteries Are Down?


Hello, I have been watching quite a few of your Marine Electrical videos on YouTube, thank you very much for producing them and sharing them with the world! I have a technical question regarding one particular aspect : My question is regarding the SOC of Lead Acid Batteries. When you say that we can take the Firefly AGM down to 20% SOC, which takes their "usable capacity" to 65% of the battery capaticy, the tested voltage at that SOC will be around 11.6V. It means that all the 12V appliances will see a lower voltage, and, if I understand correctly from some of your other videos, will have to "work" more, and will have a shorter life span.  When I talk about 12V appliances, i mean some kind of electric motors (pumps, electric autopilot, etc.)  Is that correct? Thank you. - Olivier


Hi Olivier, you are correct. As we draw a lead acid battery lower in battery capacity the battery voltage is also brought down. Some DC loads will work fine at 11.6 VDC and other DC loads (pumps, autopilot, etc) will draw more amperage at a lower battery voltage. - Jeff