Originally Posted by
seeker333
Thanks for the explanation.
I was not clear in my post. The "$7 DX charger" is an 18650 charger that charges only 1 or 2 cells on separate circuits. I would be charging cells individually, and installing and later removing from a 2s2p cell holder. I occasionally check them with meter to ensure charging OK. So the problem you described can be completely avoided by this simple process.
My point is that for a little work and ~30 bucks, you could ensure a reliable battery for your MS type light for probably hundreds of recharge cycles. And double the life for another 12 bucks for 4 additional cells. Worst thing that can happen is you throw away a cell once in a great while, at cost of 3 bucks.
I have that exact setup for my MS - a gang pack. A 2S2P holder (ie no PCB) with primo (protected) cells that are charged with a pair of cell chargers. The cells can discharge at very slightly different rates, but since they get charged to the max each time, they cannot get significantly out of balance. I actually have 6 cells which are numbered; they get rotated (1+2) + (3+4) one time; (3+4) + (5+6) etc. I log the results and am looking to see if there are 2 pair that are significantly more well matched and/or watching for a bad cell in the bunch.
Since there is always 1 pair charged, I also slapped together a 2S1P mini pack in case I need a light but forgot to recharge; OR to carry for an extra 1.5 hrs of light for late night summer rides, centuries, etc. Even with 1 pack/holder, if needed you can just carry extra cells and pop them in if needed.
One other advantage in addition to what Colleen mentioned is that the pack is reusable. I have disconnects on the connector to the pack so that to recycle it from a MS pack to a XYZ pack, all I need to do is build a new adapter/connector. They quick disconnects as the strain relief has to be removed, but still easier than splicing or rewiring the pack or building a new one. I've done the same to the NiMH packs for the other bike so the same pack can run Dinottes, Nitehawk or old Planet bike halogen and it works well as long as they are the same voltage (or close).
The down sides are a) a bit of a hassle cell charging; I dont mind the inconvenience given longer service life the pack will have and lower risk of a pack incident.
b) waterproofing. You cant heat shrink a pack you open almost every day. I am not an all weather commuter I dont need much but I put some duct tape on the outside of the MS battery bag to ward off the odd splash. If it is bad like from snow melt, put the pack in a baggie (which is just about all the protection I need).
You can also make a sleeve from a 3.00" kiddie tube but then it wont in the MS (2 strap version) holder.
All in all you loose the convenience of 1 step pack charging, but gain a lot of versatility, (should get) longer service life from the cells and little chance of pack incident.
HTH
EDIT: Ok, there is one other negative - you need to be careful to insert the cells properly to avoid short circuit or reverse polarity. Mine are clearly marked and one has some colored PVC tape to mark the positive connectors.