I honestly don’t know. Operating outside the range of the device could cause errors...or perhaps the shunt will just get warm to the touch... I do recommend that you take a reading of the shunt with a handheld IR thermometer. If you see it getting hot...I wouldn’t leave that load unattended...and would abandon that device pretty quickly. Safety is paramount.
The RV geeks did a piece quite a while back in their Winter Secret Weapon. They basically installed a dedicated branch circuit for running a space heater. It allows them to power this single outlet from the 20A gfci outlet on most pedastles. This way their heater isn’t running off the inverter, or taking anything from the power available to the other coach systems running off the shore power cord. I added an outlet like this...in our bedroom. I normally use the block heater to power it when we just use it to power a small draw like a fan. If I wanted to use a heater, or plug in a circular saw...I would run the heavy ga. extension cord to the pedastle to get the full 20A available in that outlet.
Genrally, we stick to Oasis (diesel) power for hot water and heating when running off batteries.
As far as battery measurement and health go...
The most difficult thing is Peukerts effect. In a perfect world...drawing 100A for 1 hr would remove 100aH from the battery. Unfortunately...the only point where this is true, or at least should be true is at the 20hr rate used for rating the battery. At higher amp draws...you actually take more out due to the Peukert effect. So just as a let’s say... 100A for 1 hr takes 120aH out. Not fair right? Some battery monitors can be programmed for this...others can’t. It obviously can induce error.
There are quite a few graphs which show approx. SOC for lead acid batteries at varying loads expressed as C/x... C1, C/10, etc... amps based on a fraction of battery bank capacity.
if you track this...you will get some idea of battery health. Also taking specific gravity readings from batteries which have been disconnected and allowed to rest for at least two hours.., You might regain some storage thru equalization...but it depends on how long the sulphate shave hardened on the plates as to wether or not you will see results.
I am seeing degradation on my four year old batteries. I may be getting all new Lifeline AGMs before going to the balloon fiesta next year. Until then...I can live with the degradations...as we still have plenty of amp hrs for normal use. Just really like it all when dry camping for over a week... gotta have power to run the espresso machine
if you find a large golf cart place...might see if the have one of those inductive spectroscopy devices. They can basically read your batteries capacity, and SOC in a matter of seconds using a quick load analysis. Expensive device...but if you had a large fleet of golf carts it would be nice to have.
