2s2p holder with pcm

i’ve seen this on ebay and now on FT:
2S2P 7.4V 18650 Holder with Battery Build-in PCM Protection Circuit Module

i’m thinking about building a 7.4 battery pack for a bike light like this but with quality brand cells.

does somebody know if this holder can be used to charge the batteries?
just connect the power supply like with the battery-pack?

I would hazard a guess that it doesn’t do cell balancing, so you would have to add in wires for balancing, and then use a hobby charger for charging. The only way to find out for sure is to get one and have a look at the circuit.

+1, I really doubt it does balance charging.

It’s not got enough connections for a start.

Maybe the other question is where can you get a good protection circuit for a 2s2p pack that you can wire yourself while including balance wires so you can balance charge the cell. Alternatively does it really matter if you just used protected cells?

No balance charging leads on that one. Be aware that these are very short and will barley fit some unprotected 18650 cells. I have 3 of the 1S3P carriers for my skyray king remote pack, which requires no balance charging option since its 4.2V. Build quality is fairly good on the pack, especially considering the price and that they supposedly have a protection circuit built in.

If you dont have a hobby charger for 2S2P (and want to save some money while avoiding having to solder balance leads and plug), you’d probably be better off removing the batteries from the holder to recharge them in a decent 18650 cheapo charger (assuming it charges each battery to the same voltage). Easy enough… just make sure you use a quality matching set of cells.

I wish that PCM had balance charging circuitry. That's hard to find in a 2s2p configuration.

As FlashPilot suggested, removing the cells to charge individually seems to be the best way to go here.

I agree that it probly doesn’t balance, but there is no reason why you can’t have a pack that balances and only has 2 leads if the pack contains the apropriate circutry.

you can find them, but they’re huge, heavy and expensive relative to the simple PCBs. Most of that comes from the bits needed to dissipate the voltage differential between cells as heat I’d guess (big thick bare wires). I’ve looked into it, mostly just to simplify sealing and charging my bike light packs, and it’s just not worth it for me.

I have a question. If you charge multiple 18650's in parallel, will they balance themselves out?

Of course, that’s how electricity works

The Makita 18V lithium batteries I use for work are balanced in pairs with 5 pairs in series so each pair is charged in parallel. The balancing is to keep each series set even so charging in parallel should be okay.

So this should be fine then, right?


That looks good, Glen. Might be tempted to get one as well!

It looks like very decent quality. And the price from Fasttech is incredibly low compared to everyone else. I ordered one.

BTW, I'll be using it with my iCharger 106B hobby charger along with Panasonic NCR18650 unprotected cells. Hopefully they're long enough to reach the contacts. If not I'll make copper spacers..

thanks for all your answers.

this is my problem:
I myself would just take them out and charge them individually but i’m trying to build a 2s2p pack with quality cells for a friend of mine.
Maybe i should just get the cheap 7.4V pack, strip it open, replace the cells and tape it up……
but i’m pretty sure there isn’t any balancing going on in this pack… :bigsmile:

Hi RedSpawn,

I’m in a similar situation regarding a custom battery pack in 2S2P.

What I intend to do is to charge them externally.
Batteries will be marked 1 to 4 and will be swopped in the pack in the following order after every charge.


That way there’s a full rotation on the 5th charge.

The BIG problem is getting hold of an IP68 ABS enclosure close to the size of the battery pack!