Originally Posted by MCDenny
Night Sailor, could you withdraw, say, 100 ah from your battery using the link pro to gage this. Then let the battery rest with no loads at all for several hours and then measure the voltage? That would give you the state of charge and by inference the battery's actual capacity.
Also, the peukert effect will skew your results unless you do your measured discharge at 11 amps.
I read that Gel cell no load "cut off" voltage is 11.6v. The loaded "cut off" voltage is 10.4v. My battery is going below these cut off voltage's if I use 60ah at night, which is typical for me with the furnace
and inverter running. My numbers are 11.4 and 10.2. My conclusion is I am killing this battery with these nightly 50-60 amp discharges.
I could plug in the shore power during this cold weather and keep the battery topped up until things warm up and my night time needs drop. If my night time needs drop to 25-30ah I could get some more life out of this battery.
I just started keeping records of voltage so I can't give you more info, but it seems the voltage is dropping more and more as time goes on.
What do you think? My guess is that this battery is about done in. I could possibly repurpose it as a starter battery for my rarely use generator
(mounted on a small trailer). I have another charge controller and solar panel
I could use to keep it topped up indefinitely. That seems like a better option than abusing it in my camper. I'll have to check to see if that charge controller has a gel cel option. I could make a voltage divider a regulator to drop the bias Voltage slightly and make that work.
Back to my camper. I had one 92.5ah discharge when I accidentally had the refrigerator
on AC. I did not realize it was wired to the outlet circuit. A few nights back my inverter cut off due to a low-voltage situation--the door blew open and my furnace
was working hard while I was in the house. I decided to see if the battery could handle it. Perhaps I should've plugged in my shore power connection that night. I didn't because I want to know if my battery will hold up.
In any event I have a good idea of what sort of battery capacity I need 100 amp hours seems to be a minimum number if I want to use an electric blanket. So fo lead batteries I would need double that I AH rating...or more. My solar charging capability is pretty good. Once I have the two extra panels installed I should be able to recharge my night time loads easily.
Worried about this battery I have been researching other options.
I considered 100ah lithium battery. This would be a 130 lb weight
savings. However, that might not be enough if I run an electric blanket--on medium that would be 60 watts, call it 5amps and 40 ah if I ran it all night.
Living without worries about energy use, I'll pick 100ah's as a design depth of discharge for my system. Whie lithium batteries can be depleted 90%, they don't perform well in cold weather--and I don't know way that means. They are wonderfully light
but very costly.
Another option would be an 8d 270 ah AGM, weight
savings 41 lbs. the AGM has more capacity and while gel cels have better cycle life, my experiences with them have sways been bad. The cost a lot and seem to die quickly. I would not have chosen this battery if it were not so cheap. I got it for $50.
My best bet would be two Master volt slim 200 ah batteries . Two of these would fit in my battery compartment--400ah at 238lbs. For a weight
penalty of an additional 73 lbs, I could run a 25% depth of discharge ad these would last a long long time.
The nearest equivalent lithium that would fit in my battery compartment is a 300ah 8D size at three times the cost and 3/4 the capacity and 40% the weight ( weight savings 171 lbs). Wow!
If I used only one of the master volt batteries. My weight would decrease 46 lbs and my depth of discharge would be 50%, and much less in the summer. That seems like the best option if I need a new battery.