Ryobi 18V ONE+ Battery Voltage

[Whimsey]

This is their 18V 1.5ah Lithium+ battery. Out of curiosity I checked the voltage before charging it recently and it was about 7.3V at 2 bars on the battery indicator. I charged it till the charger indicated fully charged. I checked the voltage days after I removed it from the charger and it was around 8V but showing 4 lights on the battery. I put it in my impact wrench, it ran fine. I rechecked the voltage and it was 20.3V. I let it sit for a few minutes and the voltage read ~8V. Did this multiple times and it did the same thing. My other ONE+ batteries read ~20V after charging with 4 indicator lights. Even one of the 4 ah battery that I used in the sting trimmer read 18V at 2 lights on the battery indicator. None of the other ONE+ batteries ever drop in indicated voltage just sitting. Just curious, anybody have any ideas why this is happening. I tried to contact Ryobi twice and gave up after 2 hours on hold .

 

[Greasymechtech]

The battery is dead and needs to be rebuilt or recycled

 

[fsdork]

I don't see anything in your post to indicate that there is a performance issue with the battery. Does it give the run time it should as compared to other batteries? If so, is there a problem?

Totally speculative, but could it be that there is a difference in how the battery management system in the battery performs (by design) vs. the other batteries? Is there a model or version number difference when you compare the battery labels? If there were a battery failure/degradation, it wouldn't make sense for voltage to be increased immediately following the application of a load - usually a failing battery will sag in voltage when a load is applied.

 

[Dave9]

The only thing I can think of that makes sense is that you're (some of the time) trying to use the 3rd contact to measure voltage instead of the two primary contacts.

Either that or it has a fault on the onboard BMS circuit, but if it consistently runs the tools fine (which it would not if really only producing 8V output) then I suspect the former, measuring on 3rd contact is most likely.

 

[Wolf359]

What's the model number of the battery? Some of the newer ones have more circuitry and allow for higher current draws for various tools.

 

[Whimsey]

Thanks for the reply's. I should have posted initially the battery is model P107. It operates the devices just fine, no loss of performance or battery life that I can detect. And yes I did measure the voltage on the marked - & + terminals. I just thought this is unusual and maybe someone had an explanation. Write it off as curiosity. I have a year warranty left on it, I'll use this battery primarily to see if it keeps performing ok.

 

[JHZR2]

The only thing I can think of that makes sense is that you're (some of the time) trying to use the 3rd contact to measure voltage instead of the two primary contacts.

Either that or it has a fault on the onboard BMS circuit, but if it consistently runs the tools fine (which it would not if really only producing 8V output) then I suspect the former, measuring on 3rd contact is most likely.

My first thought was that it was tested between the wrong pins.

Wonder if there’s a lower voltage that when connected to a tool causes some relay to close and make the rest of the connection.

There must be either 4 or 5 cells in series.

Wonder if they might be arranged +2 0 -2 so that each half a battery is there in a +/- configuration with a zero point center. End to end it measures 18ish volts when both halves close, but when not connected, or after a time, only half the string is there to reduce exposed voltage?

Purely speculative.

 

[DLFJ]

Found this thread in a search. I too have a Ryobi battery that shows 8V on the top terminals that mate with a tool. But it shows all 4 batt check LED's as good and runs an 18V tool just fine with full power.
I only stumbled across this as I bought an adapter ( https://smile.amazon.com/gp/product/B0B6HR7WXH/ ) to provide power to an experiment.
Odd- anyone figure out what Ryobi is up to?