Dead batteries? What am I trying to test

[Trbo323]

So, have a couple of 9.6v batteries that are having issues. While the voltage seems to be good (good ol tongue test) when I put them in a marker, they don't have enough juice to really do much. I put a normal 9v in and out does much better.

So what's going on? I have a basic multi meter, what can I test for?

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[BrickHaus]

How nice is your meter?

How many volts do the 9.6v have when measuring terminal to terminal?

Relative to a new 9v?

You almost need to load test them, but not sure the best way to try that... Maybe reading amperage output while connected to the board. This is dependent on the meter having the ability to to amp tests.

Essentially you need to make a wire harness that puts your meter in series with the circuit. Get positive of the battery to the black lead of your meter, take the red lead of the meter to the positive terminal of the board. And wire the negative of the battery to the negative of the board.

Then power up and try to fire. What kind of amp draw are you seeing? Ideally you would also be measuring battery voltage with a second meter at the same time and try to determine whats happening.

And compare a normal 9v to your faulty 9.6vs.

At the end of the day it sounds like the 9.6v has some open cells so it'll show good voltage but cant provides enough amperage to load the capacitor and or the noid.

Not sure if a 20 dollar battery is worth the efforts, but Id try all of that.

You may also have a bad charger so it stops charging too early, but the initial voltage check should show this.

[Grendel]

You want to measure the battery voltage under load. Hook up your multimeter across the battery while it is attached to your markers circuit and fire the solenoid and see where the voltage drops to. A 9.6vdc battery in reasonable condition (capacity) should be between 7.7VDC - 8.5VDC under load. If it is less then that your 9.6 VDC battery has a capacity issue (basically a V8 engine running on 7 or less cylinders). You will need to fire and hold the solenoid for a few seconds to get the meter to settle down and whatever the voltage you get if it is rapidly decreasing under load there is a good chance capacity is compromised as well.

Or buy a battery tester

https://www.amazon.com/Tenergy-Batte...xpY2s9dHJ1ZQ==

I really do not know the circuit but given it works better with a standard 9VDC battery it is unlikely the input cap is a problem but do not rule that out at this point. In most solenoid firing circuit you are not drawing current directly from the battery but instead the firing current is coming from a capacitor (they can have near infinite instantaneous current draw. A degrading cap will have less ability to store Voltage and Deliver current causing more of the current to be provided directly by they battery. Alkaline battery (standard 9V) chemistry allows higher current draw with less droop then NiMH batteries so a good NiMH battery could be hampered by a poor performing input capacitor.

[Trbo323]

Well thanks for the info but


Anyone have any suggestions for a decent multi-meter that isn't going to cost an arm and leg?

I literally started volt testing the batteries I have here and mine just gave up and died.

Awesome.

I'm doing this all for a Diablo mongoose that I have sunk way to much money into as is

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[Grendel]

ExTech are pretty good bargin basement multimeters, I even bought them for my techs in the lab so they would have a beater to use away from their benches. Here is one that should serve your needs and even has a 1.5-9VDC battery tester built in ($19). Not perfect for your 9,6V batteries but should do okay as a go/no go.

https://www.amazon.com/Extech-MN35-Digital-Mini-MultiMeter/dp/B0012VWR20/ref=sr_1_1?crid=1UKXYFKB8X5RR&keywords=extech%2Bmultimeter&nav_sdd=aps&qid=1655589567&refinements=p_36%3A1253528011&rnid=1243644011&s=hi&sprefix=extech%2Bmultimeter&sr=1-1&th=1

[ChoSanJuan]

Are you sure it's 100% the battery? A weak 9.6v battery will perform like poo compared to a fresh 9v, but since it's a Mongoose, how's that capacitor on the board?

[MrBarraclough]

I'm fairly convinced that a significant number of supposedly dead or bad boards and batteries are actually capacitor issues.

[Tarsun2]

you can hook up a resistor or computer fan or some other load to the battery similar to the marker load and read the voltage drop. this way you dont have to do any custom wiring.
you can even disconnect the positive lead from the battery to the board and alligator clip (or hold) the DMM in series on mA setting and see what it draws. (if you wanted to find something to then recreate that load)...

you can also see if you can reach the terminals while the battery is connected to the marker and read the voltage drop as you fire the marker. But in all honesty, this is allot of work for something thats already pretty much diagnosed.

to properly test a battery, you need nominal voltage, voltage under load, and test the capacity.
youre going to spend more than the cost of a new battery on the equipment needed to test the battery lol

but since you need a new DMM already, its a fun process.