Measuring battery condition
Easiest way to measure battery level of charge?
Forum Discussion
14 Replies
Freeway Flyer 05 wrote:
You also mention the terms "battery condition". There is an easy way to get a baseline for the batteries overall health. Take note of charge times. When a battery is in poor condition the voltage will spike when you try to charge it. That tricks the charger in to thinking the battery is fully charged. So the charge cycle happens much quicker than normal. Instead of charging for an hour like it normally did the bad battery will say its charged after a few minutes.
Easiest way to measure battery level of charge?
Thats a rough example. BUt just something to note. Works with any size battery. Little ATV batteries on a battery tender will turn green really quick when the battery is toast.
edit to say you can also trick the battery tender. If you are ever in a pinch and cant get a new battery just keep taking the battery tender off and on. Each time it will pump a small bit of amps into it.KD4UPL wrote:
The right way to measure the state of charge of a battery is not a voltmeter. You need a battery meter. Also known as a state of charge meter, battery gauge, etc. It involves a shunt wired into the negative battery cable to measure the current into and out of the battery over time. You program the meter with your battery capacity and the fully charged parameters and it measures current in and out and calculates the percentage state of charge. Tri-Metric is a good one. Victron makes one. Outback calls theirs the Flexnet DC. Magnum calls their the ME-BMK. Link 10 used to be one but I'm not sure they are made anymore.
As you can tell from all the previous posts, measuring just the voltage is subject to many variations. I don't know very many people who, when camping, are willing to turn off the RV, disconnect their batteries, and wait 15 minutes just to find out the SOC. A nice SOC meter with a wall mounted display is the way to go.
I would agree with this. A voltmeter is a bit like the old joke about bikinis - what it reveals is interesting, what it conceals is essential.
On my previous truck I used a Tri-Metric and the battery monitor of the Blue Sky solar controller. Now I use the battery monitor of the Magnum inverter/charger.
With AGM batteries, I cannot do a hydrometer test and, as noted, in real life my batteries are always discharging - refrigerator, heat/fans, etc. And this does not count the induction stove/microwave or the espresso machine. ;) Simply not worth the effort to disconnect all loads for a half hour or more.
But this begs the real question - what are you trying to learn and why? A common answer is, "Well, I want to know if I have to recharge my batteries." Largely irrelevant as, at least with lead acid, the answer is always "Yes!" You want to recharge any time you can, every time you can, for as long as you can. So the real issue is to be sure that you have good chargers and that they are connected so that they come on whenever they can. One of two reasons that solar is so helpful.
I tend to watch the hour counter most of all - I blow off about 125Ah overnight and I always want to see it back to 0 as soon as possible.
N.B. With lead acid, that still means that you need hours of absorb charging.
Bottom line, most of us will be better off with some form of battery monitor. The SmartGauge is the simplest.
You can learn more about the SmartGuage and all manner of other things about lead acid battery charging here: SmartGauge The SmartGauge is sold in the US by Balmar.- The right way to measure the state of charge of a battery is not a voltmeter. You need a battery meter. Also known as a state of charge meter, battery gauge, etc. It involves a shunt wired into the negative battery cable to measure the current into and out of the battery over time. You program the meter with your battery capacity and the fully charged parameters and it measures current in and out and calculates the percentage state of charge. Tri-Metric is a good one. Victron makes one. Outback calls theirs the Flexnet DC. Magnum calls their the ME-BMK. Link 10 used to be one but I'm not sure they are made anymore.
As you can tell from all the previous posts, measuring just the voltage is subject to many variations. I don't know very many people who, when camping, are willing to turn off the RV, disconnect their batteries, and wait 15 minutes just to find out the SOC. A nice SOC meter with a wall mounted display is the way to go. - Dealing with multiple disciplines is never easy.
If you yourself will spend some time with a hydrometer and verify voltage on your meter to the actual state of charge you will have a system as good as any simple measurement around. Even an amp-hour meter needs to be "zeroed" once a month, using a hydrometer.
AGM batteries are easier to manage
Lithium is impossible without an amp-hour meter system.
This is like answering a "Celestial Mechanics Made Easy
Or learning phasor algebra in 3 days question.
Or the fraudulent "Learn Spanish Using 5 Easy Tricks"
A weekend of using a voltmeter and you won't get in trouble. Try it for a month, 100% boondocking and you will end up on **** Cree. I put the asterisks in. 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.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.- 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:
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- 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. 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 !
