Protected Trustfire 18650s in series?

Hi there! I ordered a couple of cells for my RC transmitter from ebay, they were advertised as

Genuine TrustFire 3.7V 2500mAh 18650 Rechargeable Li-ion Battery

and shown was a picture of the grey unprotected 18650 cells which is what I wanted for use in series.

what they sent me however was 2 blue protected trustfire cells of the same rating.

what i am wondering is if i can use these protected cells in series.

i've looked around and I get different answers.

some people say do not use the protected ones because the pcb interferes with series operation, some say always use the protected ones because the individual cells need monitored when in series.

the ebay seller will take these cells back and exchange them for the right ones, but I have to pay the $2 shipping back which is a good chunk of what i paid for them (they gave me 50% off for a previous mixup).

if i can use these and don't need to send them back, i'd rather not.

I have used 4 protected Trustfires (flames) in series (4S1P) for over a year now. They still work well.

Only have 3 recharge cycles so far, but the protected were supplied for my 2 cell light.

RC transmitter?

I'm using two protected Trustfire 3000 Flames in series in my TR-1200 with no issues... Sometimes they will be too long for a host since you have the height of the cells combined with the height of two protection circuit boards...

Sounds like a good ebay seller John...

I use cells in series for multi cell lights no problem, but they must be decent cells some cheap eBay cells will not hold voltage well and there can be a big diffrence between cells in voltage and mAh when discharged, i can not really recomend cheap 18650's pairs off ebay even more so if you spent 4 or 5 bucks on them.

I would keep and eye on them and keep checking voltage while using them in series if you have not got a hobby charger to test them. Also some times the protection does not kick in with really low current draws. Rc radios have a low current draw around 0.100 amp give or take depending on the radio. Receivers use more due to servos and so on, but this depends on scale.

A nimh or lipo pack is normaly recommended but some lipo packs are not covered by warranty or recommended and yes they cost a higher amount. I personal use good AA nimh or after market battyery packs for rc radios due to such a low current draw cause protected lion batteries like 18650's need a higher current to work and also cause there is normaly no low voltage protection other then a warning light on the radio.

Since with rc radios you run the risk of run a ways damage or injuries it pays to make sure you use decent radio gear with failsafes and good batteries to protect your investment and people around you.

Im sure you know all this but I thought I'll post it for others to see who might not know.

They are a very good seller. A few mishaps but they are always willing to make it right.

I did go ahead and connect the cells in series and they seem to be working great.

I put the individual cells through a couple of cycles each to get the voltages matched up first, and I must say I'm pretty impressed with them at least so far.

I am using a Turnigy Accucell 6 hobby charger BTW. Great charger for the money IMO.

The cells will take around 2300mah of a rated 2500mah capacity which I don't think is too shabby for some ebay cells. I don't know if the blue ones are higher quality than the grey ones but for $8 regular price for the pair (I paid $4) it seems like a really good deal.

Time will tell.

I've got a 2s balance lead in the mail for this pack. All I need to do is connect the positive and negative on the one side and a negative on the other and the charger takes care of the rest right?

These are going into a Flysky 9x rc transmitter and I have the low voltage alarm at 6.9v for plenty of leeway. I did hear that the protection circuits don't detect really low draws (i think the 9x draws like 150ma an hour), so that should keep me safe. The transmitter functions down to 5v so I shouldn't have anything dropping out of the even if I run it a little low.

Glad the seller looks after you, the last cells i got off ebay like yours tested to 1200 mAh and the last ultra fire cells when discharge in a pair with balance leads connected the charger kept tripping out due to uneven voltage.

With the 2s balance lead the negative goes on the negative of the first battery the positive goes on the positive of the second battery and the one in the middle goes in between the positive and negative of both batteries (middle). Then your main charge leads go on like normal.

This thread might be of interest as it has pictures of what I'm talking about.

https://budgetlightforum.com/t/-/3118

Once the balance lead is connected you will truly see how they pair up when discharging. And maybe this thread below will be of some interest.

https://budgetlightforum.com/t/-/1621

It is good when the radio's have a low voltage warning i use 2.4 spectrum for air and 2.4 futaba for land and water and they have low voltage warning, but a lot of the cheap radios or RTR radios do not just a light, but like i said in my last post I'm sure you know all this i just mentioned it for the sake of others.