Replacing protected cell with unprotected cell?

[Brad808]

Hey everyone. I have a small portable speaker (doss ego II) that I've had for a few years and I'm thinking of upgrading the battery on it to have more capacity and have it longer lasting. The battery that is in there now is a single 18650 2200 mAh (which measures at 1744 mAh). I'm wanting to replace it with two 20700 3000 mAh batteries in parallel. I wired it up and it is working and physicaly fits into the speaker which is awesome, but I haven't tried charging or discharging it yet. The 18650 cell I took out is a protected cell and the 20700 pack I put into it is using unprotected cells. Is this a problem for this application? As far as I know (which is very little admitadly) the speaker is going to be handling all the charging and discharging with a low batter indicator and the cell protection is essentially a safety to prevent the cell from excessive current draw/ short circuits, etc? I was also reading that a BMS is only really required when running cells in series and not parallel?

Thanks for any insight. 

[wraper]

It's a safety hazard. If anything goes wrong with charging circuit or device gets shorted there will be orders of magnitude higher chance batteries may explode in flames as circuit preventing it is no longer there. Not to say after soldering these cells they can no longer be considered safe as they can receive a lot of damage while doing so.

[tunk]

I wouldn't do it, the speaker could rely on the BMS for both overcharging and over-discharge.

[Brad808]

It's a safety hazard. If anything goes wrong with charging circuit or device gets shorted there will be orders of magnitude higher chance batteries may explode in flames as circuit preventing it is no longer there. Not to say after soldering these cells they can no longer be considered safe as they can receive a lot of damage while doing so.

There has been no soldering on the cells they are on spot welded tabs to run in parallel (soldered onto tabs and then spot welded to cell). Can the protection circuit be taken off the 18650 cell and run inline with the new pack?

[mikerj]

 Charge and discharge currents won't change by adding more capacity so you should be able to re-use the original protection board.  Either way you should include protection.

[Brad808]

Charge and discharge currents won't change by adding more capacity so you should be able to re-use the original protection board.  Either way you should include protection.

Thanks I went ahead and installed it with the new batteries 🙂