Eric T recently posted a message containing a link to a battery monitor that plugs into a 12 volt outlet and gives measurements of what charge is left in your battery. I found the unit is only available from Amazon, and will run about $18 US with shipping. Here is the link and description:
I took some time on a recent week long trip to compare the Equus battery monitor that Eric recommended with hydrometer readings. Supposedly hydrometer readings are the most accurate method of measurement short of having expensive test equipment.
I would have to say that hydrometer readings are difficult, touchy and the instruments suffer from poor quality. It took me two purchases to find a working model and the second model is going back as it has filled itself with battery acid and it cannot be easily drained. It is also made of glass. The inexpensive hydrometers give readings on a scale with tick marks between numbers, the glass insert must be balanced so it is floating in the acid you have drawn from the battery. In addition, you must add or subtract depending on what the thermometer tells you. In all, I felt a cumbersome process that is easily skewed. There may be better models available but after visiting four stores I felt I selected the best available, it was less than $6.
Below is a table of what I found with readings from the Equus battery monitor and a hydrometer test. As you can see there is a pretty good correlation of results. I really distrust the hydrometer readings because there is so much chance for error and obtaining a precise reading.
Day Hydrometer Battery Monitor
1 1.281 13.14
2 n/a 12.59
3 1.277 12.57
4 n/a 12.47
5 1.252 12.45
6 n/a 12.30
7 1.221 12.32
From this table you can see my usage over the 7 days, we are running all led lighting but soft white, which is not as energy efficent. My son uses a CPAP at night, in researching his model it draws very little when in the 12 volt mode. The water pump and Max fan would be the only other draw. There seems to be a pretty strong correlation between both instruments and the results.
It is recommended that you not draw a battery below 12.00 on a regular basis as that will shorten the battery life. Assuming that the battery declined the second two weeks at the same rate we could get two weeks out of this new pair of 6 volt batteries.
In conclusion, if you boondock and want to monitor your battery this definitely beats the four colored ledís on the Escape monitor panel. You have a precise number and can even tell what power a particular device is drawing by running it and seeing the monitor change. I recommend a hydrometer for occasional (seasonal) testing on all the cells on your battery but if you want to easily watch your battery the Equus batttery monitor does the trick.
Thank you Eric for the recommendation.
Note: I have no connection with Equus or Amazon.