David, not having your breadth of knowledge "If say it takes 3 hours to go down to 12V, that will mean the
battery has dropped from 100Ah to 30Ah." is that god or bad?
I should have said the CAPACITY has dropped from 100Ah to 30Ah - so
battery is goosed in that situation!
And this is why the charging appears to be working so well as you *think* you are recharging a 100Ah
battery but you are really recharging a piddly little 30Ah
battery in effect.
And how would you actually do this "put a set load on it of around 5A per 100Ah of nominal capacity"
Find something that draws that load and switch it on. it is that simple. A good way if you have an
inverter is plug in a simple old-fashioned lightbulb. a 5A load at a nominal 12V is 60W - so say you are testing a 100Ah
battery and use an
inverter for the test, a 40W bulb or a 60W bulb will give you a set power load - one a bit less and one a bit more than 5A DC (with
inverter overhead), but just a matter of doing the maths....
Load of x Amps multiplied by y hours before voltage drops to 12.0V = z AmpHours drawn. multiply that Amphours value by two gives you the current total capacity of the
battery. It is generally considered that when the current max total capacity of a
battery has dropped by 18% (I think that is the accepted value?) of the design capacity, the
battery is gone and should be replaced.
the 12.0V could vary depending on the type of
battery but it is a close enough value to get a good feeling. basic lead acid is 12.04V at 50% and under a load there is a sag so 12.0V is a nice rememorable number to use.
Asking for a friend as I know my LB is goosed but it has been for 3 years but still does what we need.
My own motorhome was similar to barrys .... came with two good brand batteries and the voltage was decent but the pair of 120Ah batteries lasted one evening on the first trip away. I was planning on upgrading anyway (like barry), but I thought I would have had a bit more time to plan it (as did barry
![Smile :) :)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
).
If someone tends to use EHU when camping (like the owner of my Motorhome did), then a knackered
battery can still be enough to use betwen site A and site B.