Bike light battery connectors... and the batteries (18650 Li-Ion)

I was going to try to solder bike light batteries I have that died simply because the wires broke, but that got too dicey for a clueless person like me.

I have several bike lights by different manufacturers. They all have very similar connectors on the lights/batteries/chargers…but not identical. If I recall, when I had two that were working, one of the batteries could work on both lights, but only be charged by one of the chargers, something like that.

Was this just poor workmanship, or are these connectors different and how do I know which is which if they are different? Since I can’t find much in the way of reference to the connectors, my guess is that they are supposed to be interchangeable?

The actual batteries are all the same: 18650x2 or x4, each 3.7 volt. (I don’t understand what any of that means, I just know that they are all the same kind of basic batteries that have been somehow combined) And what gives me longer life? More batteries (a 6pack of the same vs. a 2pack?) or the MAH number? (Which many people say is untrustworthy)

Some examples: (the connectors all LOOK the same as my connectors, but even my connectors are not identical, although they can be used as I described)

I have reason to be using these lights a great deal, so I would like a few batteries ready to go or a couple of really long-lasting batteries. But of course I want them to work with the lights I have…der…

18650 is a form factor for a cell. 18 mm diameter and 65 mm long. It doesn’t say anything about the battery chemistry, but Li-Ion is the usual one.

Energy is just mAh * nominal voltage * cell count. For a given form factor, though, the mAh rating doesn’t change much and for a given chemistry the voltage doesn’t change. And as you said, the mAh ratings are very inflated. To a first approximation, you can assume that a pack made of 18650 cells will have energy proportional to the cell count.

You can’t just sub in a 4-cell pack for a 2-cell one, though, since the voltage will be different. The bike light may or may not be compatible with a higher voltage; you need to check the specs to be sure.

In your position, I would switch to packs made for RC vehicles. They are cheap and interchangeable. The connectors are not quite what you need, but you can get the connector from a real light pack, solder another standardized connector to it, and then use that as a jumper to go from pack to light. This will require some minor soldering, but it’s easy and there’s no chance of damaging the cells through heat.

So what you can do is get a bunch of these:

Then, get some of these:

Or these:

These are just examples of course; you can look around for others. The important bit is that “4S” means four cells in series, for roughly 43.7=14.8 v, while 2S means 23.7=7.4 v.

Once you have a working setup, you can substitute in even larger packs for long trips, or smaller ones for shorter ones, etc. Just a thought.

Umm, Doc… I’ve got pretty much no idea what the hell you are talking about, for the most part. I do appreciate the effort, however! :slight_smile:

Yeah, and soldering is exactly what I don’t want to do. If I was gonna mess with that I would just fix what I have.

You seem to be quite well versed… do you happen to know the answer to the question about the connectors? I don’t even know what they are called but the seem to be kinda standardish…

They all look to have some form of a weather-shielded coaxial power connector. These are very common for low voltage DC applications but are totally non-standardized. Even the polarity may differ between applications.

It can be dangerous to mix and match packs since even if the connector dimensions allow it to physically fit, the voltage or polarity may be very wrong. If you don’t have much skill in basic electronics, the only safe way to proceed is to buy a pack from the original manufacturer.

The packs you linked do at least say they are 8.4 volts, which means they all have two cells in series, with the larger packs having more cells in parallel. They don’t say if the connector is “center pin positive”. You can try one of these packs, but I would get/borrow a cheap multimeter to ensure that the polarity is correct before plugging it in.