LiPo dumps fast

[Frankentruck]

I pulled out my trusty B4 street basher with 550 12T brushed motor and XL5 ESC. Charged up my #1 (ID added so I can keep track) 2s 50c 4000mah LiPo stick pack... and 2 min later the fun was over. The battery had dropped to the cutoff voltage. Weird. Charged up my #2 and and gave it a go. 1 min later it was dumped. Could it be the motor being too large of a current draw? Charged up #2 again and went for a run in the Super Clod. 6 min later the fun? as over. Maybe my $20 each cheapo batteries are done? Maybe my maintenance plans of sometimes leave them charged sometimes don't has doomed my batteries? They both charge to an 8.4v peak really fast at 4 0A on my Tenergy charger, much faster than they used to. They also feel slightly thicker in the middle (measure almost 0.1" thicker) than at the ends. Sound like the batteries are junk now? #1 probably has 30 charges over the last 2.5 yrs, and #2 probably 15 charges.
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[kandkhobby13]

My guess is the battery is done for. The cells have probably deteriorated or built up a lot of resistance, especially if they 2+ years old. I've seen a lot of batteries over the years that look normal, have matching cells, and charge fine but when you go to run them either die out quick like your describing or just have no power at all.

[XLR8]

What are your cell voltages? If they differ more than say .3 volts, that could point to a weak cell and result in short run times. I've had it happen with cheap 2s and 3s batteries despite always keeping my batteries on storage charge and always balance charging them just prior to using them.

[Frankentruck]

The cells are within .02v of each other, typically ending up at 3.88v each.

[RogueIV]

how much mAh does the charge claim it's charging to?

The battery could just be bad, looks like a amazon special right? Some of those are notorious for improper mAh ratings and just poor quality.

Also willing to bet that deans plug knockoff is actually made of steel and not copper, see if a magnet sticks to it, if so it's a crappy counterfeit deans and probably has way too much resistance.

[silvertriple]

The cells are within .02v of each other, typically ending up at 3.88v each.

That's a bit high for a lipo cut-off : it should be around 3.3V each.
My assumption : gearing is too long, and result in ESC/Motor heating up fast, resulting in thermal cut-off...

NB : I have a Traxxas Slash 4WD with a Velineon VXL 3500. I never reached the lipo cut off with this car, it was always a Thermal cut-off...

[Frankentruck]

how much mAh does the charge claim it's charging to?

The battery could just be bad, looks like a amazon special right? Some of those are notorious for improper mAh ratings and just poor quality.

Also willing to bet that deans plug knockoff is actually made of steel and not copper, see if a magnet sticks to it, if so it's a crappy counterfeit deans and probably has way too much resistance.

The batteries are from Amazon. They still worked great a couple of months ago The battery connectors don't seem to be magnetic.

I hadn't been paying attention to the mah state that the charger was claiming. I might need to experiment a little.

The cells are within .02v of each other, typically ending up at 3.88v each.

That's a bit high for a lipo cut-off : it should be around 3.3V each.
My assumption : gearing is too long, and result in ESC/Motor heating up fast, resulting in thermal cut-off...

Both the Traxxas XL5 and the HW880 ESCs are cutting off at this voltage. I checked the XL5 when the cutoff dropped the buggy speed. It was not hot. The motor wasn't very hot either.

[silvertriple]

how much mAh does the charge claim it's charging to?

The battery could just be bad, looks like a amazon special right? Some of those are notorious for improper mAh ratings and just poor quality.

Also willing to bet that deans plug knockoff is actually made of steel and not copper, see if a magnet sticks to it, if so it's a crappy counterfeit deans and probably has way too much resistance.

The batteries are from Amazon. They still worked great a couple of months ago The battery connectors don't seem to be magnetic.

I hadn't been paying attention to the mah state that the charger was claiming. I might need to experiment a little.

The cells are within .02v of each other, typically ending up at 3.88v each.

That's a bit high for a lipo cut-off : it should be around 3.3V each.
My assumption : gearing is too long, and result in ESC/Motor heating up fast, resulting in thermal cut-off...

Both the Traxxas XL5 and the HW880 ESCs are cutting off at this voltage. I checked the XL5 when the cutoff dropped the buggy speed. It was not hot. The motor wasn't very hot either.

I use the same batteries. No issue so far. I pay attention to put them in storage at the end of each week-ends of runs and I do not have any issues. Always balance charged at 1C (4000mAH), I generally run the same pack twice or 3 times within a week-end (with a balance charge at 1C) between each run, and at the end finish by a Storage charge (either on site, either once at home). Lipo don't like to be stored full or empty. The cell voltage should never go lower than 3.0V per cell. When I have the choice, I set the lipo cut off at 3.3V, and generally, I stop runs before that (it's about 3.5 V per cell when I stop)...

[Frankentruck]

What does balance charged at 1c mean? I did see my charger was defaulting to 3000mah instead of 4000mah.

[silvertriple]

What does balance charged at 1c mean? I did see my charger was defaulting to 3000mah instead of 4000mah.

Balance charge at 1C : Charge max 4000mAh (that corresponds to the battery capacity), while ensuring each cell have the same voltage... Not all chargers are the same, and there is another mode on my charger, where it pushes 4000mAh permanently to the battery until it hits the target voltage - I don't use it. Check your charger manual to see how it behaves...

[RogueIV]

1c is the charge rate compared to the mAh of the battery. a 4000mAh battery should be charged at 4amps. max voltage for a normal lipo around 4.2volts per cell.

If it's cutting off at 3.88v per cell during use and the battery is getting hot it could mean that he internal resistance is really high (it's probably going below the cutoff voltage under load) and you should retire the battery pack as it could potentially overheat and start on fire.

Also if the cells are getting puffy that's also a good indicator that the battery is past it's prime.

[Frankentruck]

Thanks for the 1c explanation.

The batteries aren't getting hot, but 2 different vehicles are cutting off way too soon. The batteries are probably no longer usable, but maybe I'll do some discharge and charge cycles to see if they revive.

[Elkcycles]

Unlike nickel cells, you really can't revive a LiPo.

[Frankentruck]

Yeah, after discharge and recharge the 4000mah battery supposedly charged to 1845mah.

[RC10th]

Possibly try another charger if it's multiple batteries playing up. I would double check the the individual cell voltage manually to confirm.

I don't normally recommend it but IF the cell voltage IS balanced you could try charging it without a balance charge, you'll need to keep a watchful eye (checking voltage periodically) or charge it outside incase anything funny happens, however, I would just try a different charger first