Are My Batteries' Capacities Overrated??

[Tommy R]

I've got an interesting problem. I'm running 1750 mAh 3s batteries in my scaler. My LiPo cutoff is set to 3.0 or 3.1v/cell. I was running my truck the other day 'til the battery cutoff kicked in. When I charged it back up, it only took 1000 mAh. Is that normal? That means the battery was only at a little less than half capacity when it cut out.

I thought it would take more than 1000 mAh to fully charge a dead 1750 mAh battery. It now has me wondering if these "1750" batteries are overrated? They came from Hobby City so it certainly wouldn't surprise me. Rhino is the brand.

FYI, I run these in parallel in my 2.2 scaler for a capacity of 3500 mAh, in case that makes any difference.

How many mAh do you typically put back into your dead batteries?

[Tomy]

Rhino batteries are usually good quality. What was the voltage of your empty batteries before you started to charge them?

[Tommy R]

I don't recall specifically, but I did measure them and they were in the 3.75v range, give or take. If the voltage cutoff is at, say, 3.1v shouldn't that be the reading I get when I measure them? Maybe my voltage cutoff came in prematurely?

[indiana mudcat]

May not be the case. But if the batts are not enough "C" rating, under a high amp draw like a bind pack voltage drops fast, LVC kicks on then the pack recovers when the draw stops. I've had 1900 20c peak packs that would hit LVC with a full charge, then only take 100mah to recharge. Cold weather makes this effect worse.

[Tommy R]

Originally Posted by indiana mudcat

May not be the case. But if the batts are not enough "C" rating, under a high amp draw like a bind pack voltage drops fast, LVC kicks on then the pack recovers when the draw stops. I've had 1900 20c peak packs that would hit LVC with a full charge, then only take 100mah to recharge. Cold weather makes this effect worse.

That's a good point! These are about 20c if I recall (again, two batteries in parallel). And I was having drivetrain binding issues I was unaware of at the time. I guess it would make sense that the current draw would be more than normal. So even though I was just trying to drive it, it was still struggling and maybe pulling too much current for the batteries. Very interesting stuff!

[Tomy]

Originally Posted by indiana mudcat

May not be the case. But if the batts are not enough "C" rating, under a high amp draw like a bind pack voltage drops fast, LVC kicks on then the pack recovers when the draw stops. I've had 1900 20c peak packs that would hit LVC with a full charge, then only take 100mah to recharge. Cold weather makes this effect worse.

x2

I had this issue with my SC-truck on old batteries. Bet this might very well be your issue, too.

On my crawlers I have my cut-off set at 3.1V and the cells are usually at 3.2V at the start of a charge.

[Tommy R]

Originally Posted by Tomy

x2

I had this issue with my SC-truck on old batteries. Bet this might very well be your issue, too.

On my crawlers I have my cut-off set at 3.1V and the cells are usually at 3.2V at the start of a charge.

Thanks for the info. What kind of c rating are your batteries? This might be another good reason to buy batteries with higher c ratings!

[Tomy]

Originally Posted by Tommy R

Thanks for the info. What kind of c rating are your batteries? This might be another good reason to buy batteries with higher c ratings!

I try to use batteries with at least a 30C continuous c-rating. The batteries I was referring to are 45C continuous and 90C peak 3S 800mAh Lipos.

[Erin]

Dont forget, unless you check voltage immeadiately after cutoff, it will come up some.

My 3s 1050 rhinos typical take close to full mah or alil more when packs at 9volts, but they are 40c's. My 1350's are 30c's and never had trouble w those either. Always charge at 2c if that makes a difference, but i doubt it.

[Manning]

Old packs will display the same tendencies as Mudcat explained as well. Batteries wear out with use and time.

[Tommy R]

I hadn't considered age being a factor. These batteries are all more than 1.5 years old and were cheap. Maybe they're showing their age now by losing capacity?