Battery question

Normal. 13.5 is charging, 12.7 full charge resting, 12.2 60% charge in use. You are good to go and the solar is working well for you.

The 12 Volt Side of Life

You’re saying it reads 12.5v in the morning but won’t run the heater.
Doesn’t make sense. Or are you saying you run the heater and kill the battery quickly?

turn the heater on from a minute or two to "shed" the surface charge, then take a voltmeter reading... or better yet get a good quality hydrometer.

12.5 volts should be enough to run the heater. Maybe check the voltage while a helper turns on the heater.

RE Cheep meters.. Now long ago and far away (Well not that far,,,Tekonsha MI and I'm not near (but not in) FLint) I had a very nice very "Consistant" Vacuum Tube Volt Meter (RCA WV77e)

It came with calibration instructions Today I use hand held not plug in meters. But the calibration test procedure should still work.. A brand new Carbon Zinc D-cell (Well you could use an aaa for that matter but the D will give a more accurate calibration on a cheap meter. Alas. What I forget is the voltage. I do recall it is not 1.5 but something else The manual for the WV77e Will tell you what it is

For a full lab calibration there are several things used

A variable voltage source hooked to a mercury cell via a Galvanometer (Amazing I got the spelling right) Hook meter under test to the variable source and adjust so the very very very very sensitive Galvanometer shows NO current flow.. Reading on meter should be voltage stamped on mercury cell.

Done that too.. 50 years ago.

I would not suspect a meter is the issue. I have never seen a bad one, but maybe there are bad ones.

Will your heater run at sunset? Will it run in the daytime?

Check that the wiring going to the heater is sufficient. Sometimes wires get broken (where there is just a few strands left), or corroded, and the wire can no longer carry the amps needed to power the propane fan motor (I think is what you have, not a electric one)

The fan motor on a propane heater should run even below 12 volts, though audibly slower.

Grit dog wrote:
You’re saying it reads 12.5v in the morning but won’t run the heater.
Doesn’t make sense. Or are you saying you run the heater and kill the battery quickly?

It will run the heater fine but kills the battery quickly.

time2roll wrote:
Normal. 13.5 is charging, 12.7 full charge resting, 12.2 60% charge in use. You are good to go and the solar is working well for you.

The 12 Volt Side of Life

Good read, thanks for posting.

It will run the heater fine but kills the battery quicklyIt will run the heater fine but kills the battery quickly.

I cannot help further.
The heater motor is a big amp draw, but should run off and on all night then be dead by morning. I have two batteries and even when they were new the heater would draw down the voltage quickly. On very cold nights when it would run half the time both batts would be pretty low by morning and the lights would be half as dim,though I had an ARB electric fridge running too, but it would not draw a lot of power on a cold night.

I would take the battery in to a auto parts store and have them load test it. Those test are not perfect, but will possibly identify issues. They will also want to fully charge it with a high quality batt charger, so you leave it, let them charge it, then they test it. At the least you get a free quality charge…