When to Charge

[limmer]

at what voltage should you start charging? for some reason I remember on a charter I did in BVI they told me to charge the batteries when the monitor said 10.5V but I have read here that at 12.0V is when charging should start. Can anyone shed any light on this for me. what would be a safe voltage to start charging? cheers limmer

[Cheechako]

hmmm.... I cant remember state of charge but 10.5 is pretty much completely dead and gone! 12v sounds pretty close, however on most boats, my experience has been it's hard to stay up to 12v overnight. Isnt 11.5v 50% discharge...?

[Sailabel]

Hi Limmer- the key for battery longevity is to not let the battery bank become less than 50% discharged. 10.5 volts is discharged.... I'm sure that someone will chime in soon with the voltage for 50% discharge.

You may want to consider eventually installing a battery bank monitor that will let you know when the batteries are 50% discharged... ours reads in amp-hours used and % capacity remaining. There are several options/manufacturers for the monitors.

For capacity and longevity, we ditched the 2-bank house system and wired for one large battery bank, plus a separate/isolated starting battery. This allows us more amp-hour capacity for house loads while reducing the depth of discharge on house bank.

Steve

[Cheechako]

It's complicated, but for Trojan Deep Cycle Gr27, at rest, it is: 12v = 25% charged, 12.3 volts = 50% charged , 12.5 volts = 70% charged.

definition of At Rest: "6 lead-acid cells in series and at Rest. “At Rest” means
that no current is moving through the cells, i.e., that
they are neither being charged or discharged.
Determining a battery’s state of charge from voltage
measurement is vague enough if current is moving
through the battery. The vagaries increase
exponentially if no current is moving through the

battery."

[Rhosyn Mor]

I am not too sure about other kinds but my Gel 8D's ( not AGM) are dead at 11.8V.
I deep discharge them down to 12.4 about once every couple of months, the rest of the time the solar panel keeps up with my usage and they pretty much stay at float voltage of 13.1