Why isn't battery polarity always the same in JST pins?

I’ve seen batteries with JST connector with the positive (red) on the right side:

And some others with positive (red) on the left side:

Why isn’t battery polarity always the same in JST pins?

There’s no standard for it. That battery looks to be reversed.

Particle, Sparkfun and Adafruit use the same polarity on the JST-PH connector.

On the battery side, with the key facing up, and the holes facing you, the right side is +.


Note that you can swap polarity if you’re careful - use a sharp tool to lift up the plastic latch (underside on the photo above) and the wire will pull out. Pull one out, insulate it, then pull the other out, and swap them over.

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Here is the dirty little gotcha with JST PH2 connectors that is rarely noted beyond a passing sentence. Pay close attention here and be safe or experience poof (the release of the magic smoke) here and there, or worse.

TLDR; jump to the RC vs IoT section below

The RC industry (right or wrong) which has been active for a long time, set a standard for connector polarity, for certain new or existing connectors. Other industries (newer or older, right ir wrong) use the same polarity and still others don’t. This can bite you if you are not prepared. Be repared!

Most batteries, pigtails, and charges found on popular consumer sites, like eBay and Amazon, cater to RC-related buyers - but this will soon change as IoT grows and RC shrinks.

Buy a battery (or charger or pigtails) on Amazon or eBay (or an RC site) and it will probably be slanted towards consumer-based RC needs, and this can get you good, if you are in IoT-thinking at the monent.

The fancy term for this is domain-specific context or knowledge. Meaning it is best to know the context of a discussion, purchase or interaction, and never assume otherwise.

Here are the common (never 100%) differences that you too can verify yourself by searching at sites geared towards RC and IoT:

=== RC vs IoT ===
Usually these trends below are found (but don’t assume “Always”):

– RC
Looking at load side (female shell with male pins)
Key/slot up
Red (+) is on the right

– IoT (and many other electronic industries)
Looking at load side (female shell with male pins)
Key/slot up
Black (-) is on the right

!! Safety !!
One can’t say who is to blame here but this is a good example of many industries (early on when new), not wanting to take the time to think about existing standards as much (or even a litte) as running to market with a product or creating a look-what-I-did demo and having that demo escape without further (slowing down and taking a breath).

Not all devices have reverse-polarity protection so if you don’t look twice before connecting, you may damage your device or experience a LiPo fire - so please be carefule. Always lean on the side of safety and use a fire box or pouch when possible. Do not assume polarity with new connections, and then rapidly connect things for the first time, while being next to flammable items and walk-away.

When in doubt, take a breath, measure twice and cut (plug) once, and things won’t turn out messy.

Happy Wiring

It is true. The polarity of Particle batteries matches those used by Adafruit and SparkFun, but it is opposite of many RC batteries.

There is a guide to Particle LiPo batteries, including how to switch the polarity of a JST-PH connector here: