Measuring battery condition
Easiest way to measure battery level of charge?
Forum Discussion
- There is the right way (install a proper voltmeter), and then there is my way -- I disconnect the battery. Let it sit for 15 min. Take out my little multimeter and hook it up.
They say you need to leave the battery resting for quite a while to get an accurate reading. But I tried taking a resting reading after 5 min, 10 min, 15 min, 30 min., etc., and found that the reading was very close to correct after only 15 min.
If you try to take a reading when the battery is connected to your RV, you will probably get an artificially low reading. It'll say 12.2 volts when it is really 12.5, for example. - best SOC indicator is measuring specific gravity with a calibrated hydrometer with temperature compensation. Look for a Frease (sp?) brand hydrometer.
The cheap ones in the auto parts store are hit and miss
If you want to know battery condition then after fully charging the battery to a load test. - It depends on the type of battery, and few methods work for all types of batteries.
You can't measure SOC with any accuracy using a voltage measurement on a Lithium-Ion battery.
You can't measure SOC using specific gravity on a sealed battery.
But if you start with what you know is a fully charged battery and use a permanently attached coulometer to measure the power in and power out, it will give you a pretty good idea of your battery's SOC at any point in time. - If you install a solar system with a display, during daylight hours you can tell the SOC by the amount of current the batteries are accepting.
profdant139 wrote:
There is the right way (install a proper voltmeter), and then there is my way -- I disconnect the battery. Let it sit for 15 min. Take out my little multimeter and hook it up.
Concur ! At least 15 minutes, 30 is better !- I have used an Innova battery monitor for years. It plugs into the 12V cigarette lighter type of 12V outlet and is movable, so I can use it to see voltage for car, RV chassis battery, or RV coach battery.
Amazon has them for about $12. Freeway Flyer 05 wrote:
Condition, capacity or state of charge?
Easiest way to measure battery level of charge?
Or when to start or stop the charging process?
Please post what you are experiencing and what your expectations are.
More details on the number of batteries and even the type of battery would help.
I have just used a voltmeter for a long time. Works fine.
The 12 Volt Side of Life- This can get quite complex.
-- Voltage gives an indication of the state of charge, but it is not reliable. Under load the voltage will be low, under charge, it will read too high.
-- The usual way to handle this is with an hour counting meter, the Trimetric from Bogart is one of the best known. The easiest to use and install used to be the Smartgauge, now replaced with this: SG200
If you have lithium batteries, be sure that whatever you buy will work with them.
Knowing the state of charge of your battery is interesting, but not very important. What IS important is that your CHARGER knows the state of charge and begins charging whenever needed.
Lots of info, if now a bit dated, on my site, under "documents." Freeway Flyer 05 wrote:
Easiest way to measure battery level of charge?
There are 3 ways
Best. for flooded wet cells. Hydrometer Measure the specific gravity and consult the chart.
Easiest for all: Voltage. RESTING voltage at least 30 minutes of no current flow
Hardest but 2nd best is a computer that tracks every fraction of an amp hour in and out of the battery and is properly calibrated .
The problem with this is as the batteries age capacity changes and the computer needs re-calibration.DiploStrat wrote:
-- Voltage gives an indication of the state of charge, but it is not reliable. Under load the voltage will be low, under charge, it will read too high.
Which is why you disconnect it from everything and let it rest for at least 15 minutes.
