Spare lighter battery unit?

I purchased a torch recently that came with spare batteries, I was wanting one plus a possible spare for my T-Beam Tracker?

I then had an idea?

one of these

add four of these

and I end up with this?

any thoughts on using it as a spare power supply for the 817 instead of a 3Ah SLAB?



You need only 3 not 4 of those batteries for an 817.Also the battery holders with the sping connectors often do not make good contact with the ends and so limit the current you can pull.


Thanks Andy, so 11.1 volts rather than 14.8v and create a better connection for them.

I also take it because they are Li-on batteries, they won’t give me much time especially on TX at 2.5 watts?


When they are full they are 4.2V, so 3x 4.2 = 12.6v 4x 4.2 = 16.8V which is above the absolute maximum voltage. The 817 is cleverly designed so that it gives full output power down to about 10.2V.

Ensure those springs make good contact and keep them and the cell electrodes clean so you don’t get any voltage drop at higher currents.


Got you, yes that measurement on the meter was before I stuck them in the Charging unit. I am full of schoolboy errors me :face_with_peeking_eye:

okay back to bench to reform the project.

as always , yourself and others on here have the skills to point me in the right direction

Cheers Tony


I use the 3 cell version of the holder with recovered 18650’s from old laptop batteries. These cells are typically 2000mAh. I made up a harness with powerpole connectors to wire these holders in parallel to bump up the power rating if necessary. I have had no obvious issues with the spring contacts, as all batteries seem to be equally discharged after use. 1 pack for the KX1, 2 packs on the KX3. I haven’t run them flat yet.


All sorted, made a 3 battery holder from the 4, and 12.4 volts on the multimeter :+1:

Will test it out this weekend :crossed_fingers:


Hi, use this for my 818, 3x18650 with fuse and BMS. But finally I made another with 6 cells (2 serial strings in paralell) to get more amp.


I used those 4-battery holders for years. Recommend replacing the wire on them with something thicker as they get quite soft in tx even with just the ft818,especially when spotting using sotamat/ft8.

The springs couldn’t cope with my 20w amp - melted back through the plastic case.

I find these more reliable:

Glue 2 together and put a link in to make them 3-4 in series.

I run 1 set for radio and separate for amp, if I need one.



I have 3d printed a holder to replace the FT818 internal battery, also holds a BMS circuit, and provides direct connection using the internal plug in the ft818.