Battery health--how to tell good from bad?

[5r49cfu]

broke out the Solo the other day, what a great machine to fly!

Had three batteries, all with about 10 cycles, all manufactured at the end of 2015.

One of my batteries drained from 100% to 30% in about 30 seconds, not good obviously.

Two other batts were just fine, held their charge for the normal amount of time (10m or so).

I used the madhacker.org tool, but no red flags on the "bad" battery. Health data is limited.

What should I look for when flying to know if a battery is bad (aside from that quick drop in %)?

 

[Frank Foster]

Now that you bring this up, it got me to thinking. I don't think I have ever seen or heard of any kind of "load tester" for lipo batteries. Like the battery testers made for car batteries, where you actually put a load on the battery, and see the results on a meter. Otherwise, I guess the only way to tell the health of a battery is by checking the charge rate/time, and like you said, the amount of time it holds that charge. I've had one Solo battery go bad, probably because it was drained too low. It had swelled up, and would not charge. When I opened up the pack, the cells quickly swelled up like little balloons!

 

[VCD]

With the said madhacker tool:
if you started out with a fully charged battery - then flew it down to 10-20% SoC - the battery's BMS would update it's actual capacity.
Then you connect the madhacker tool - and read out Act.Cap (Actual Capacity) - The battery's design capacity is 5.2Ah , if you see 3,6Ah - then you know it's only 70% of it's original capacity (and flight time)
All you need to know is there.

 

[5r49cfu]

With the said madhacker tool:
if you started out with a fully charged battery - then flew it down to 10-20% SoC - the battery's BMS would update it's actual capacity.
Then you connect the madhacker tool - and read out Act.Cap (Actual Capacity) - The battery's design capacity is 5.2Ah , if you see 3,6Ah - then you know it's only 70% of it's original capacity (and flight time)
All you need to know is there.

hi VCD,

According to the mad hacker tool, the battery that drained quickly is down at 28% (16.12V, 1456mAh

Des C: 5200 mAH
Act C: 5153 mAH
Rel Chg: 28%
Abs Chg: 28%

So it didn't reset the max capacity to something lower.

 

[SKuhn68]

Testing actual battery capacity and viability comes down to measuring its internal resistance. That is about all I can tell you, the finer details are above my paygrade. But that should get you headed in the right direction for your research.
SKuhn68

 

[VCD]

@5r49cfu So your battery is a bit degraded already, you may expect the Act.C to drop further over time. As it does, you will usually observe that the 25..0 State-of-charge percents drops off faster than expected (the curve is logarithmic)

@SKuhn68 Yes, and no, the internal resistance is a good way to quantify the heath of a battery, (provided that you know the Ir of the pack when new) - but then there is no standard for how such tests are performed (the current and time) - for example, some battery testers use 100mA , 100ms and there is a lot of variation, making comparisons (and result) impractical.

As we fly a Solo, which has usually the same TOW, and the power required for cruise/hover is about the same - the only real measurement we *need* is "how much capacity can the pack deliver at this load" and that's what the internal BMS does - it's counting mAh - until the voltage gets low... this measurement compensates for internal resistance, as when internal resistance increases, you will see less mAh being spent before it's "empty"

In other words: it logs for example 5000mAh actual capacity (this is at 20A) - if the test was performed at 1A , you would get much more than 5Ah out of the pack.

Hence, actual capacity, measured in flight - is a good representation of the battery's health.

 

[fourprops]

broke out the Solo the other day, what a great machine to fly!

Had three batteries, all with about 10 cycles, all manufactured at the end of 2015.

One of my batteries drained from 100% to 30% in about 30 seconds, not good obviously.

Two other batts were just fine, held their charge for the normal amount of time (10m or so).

I used the madhacker.org tool, but no red flags on the "bad" battery. Health data is limited.

What should I look for when flying to know if a battery is bad (aside from that quick drop in %)?

The bottom line is when these 2015 made batteries crap out, that's it. No company is making a replacement battery.

 

[VCD]

yes, the closest to a replacement is BMSOne and a Tattu battery (or any suitable Li-Ion or Li-Po battery.) - but then you can fly with "any" type of battery. (no longer limited to a battery made for Solo)

 

[5r49cfu]

had another battery go bad the other day, luckily it happened once I was landing.

the percent just started nose diving from 50% down to 6% when I landed.

Using mad hacker tool afterwards, the resting percentage was ~65%

that one is going in the bad pile

 

[VCD]

@5r49 the BMS inside Solo batteries seems to update it's capacity when reaching a certain low voltage - it should not bounce the SoC back up.
Can you post the dataflash-log from the Solo? - or even the .tlog ?