Hi all,

AI'm asking this for understanding.

I have a 4 pin battery/charger. Charger pins are as follows:

1 = unused

2 = positive (brown wire)

3 = negative (blue wire)

4 = unused

If I ever need to purchase in future (if all other specs are compatible), how determine which wires are positive and negative?

Edited Sunday at 09:413 days by urbanCyclist

How about going to Screwfix and buying a cheap multimeter - less than £20.

On 25/04/2026 at 14:30, urbanCyclist said:

Hi all,

AI'm asking this for understanding.

I have a 4 pin battery/charger. Charger pins are as follows:

1 = unused

2 = positive (brown wire)

3 = negative (blue wire)

4 = unused

If I ever need to purchase in future (if all other specs are compatible), how determine which wires are positive and negative?

How did you figure out that two are unused? If you opened the connector and saw only two wires connected, then you can use any charger you want as long as it has exactly the same charge voltage and the current is within 1 amp of the present one.

If you get another charger with a different connector, you can swap over the connector, but you MUST check the polarity of the wires with a meter. DO NOT go by the colours because I've had more than one Chinese charger that used the blue as the positive and brown as the negative.

+1 for the multimeter, once in your toolkit you will find it useful in many ways.. some dont even need the intimidating dial that know one fully understands when first getting one;) and will automatically work out what your measuring and apply the relevant metric and scale ta-da!!

But i will mention that being able to turn the dial to the one or two settings you understand ok with a determined click will make all the ladies go weak at the knees ;)

Joking aside reading the battery's actual voltage with a meter rather than the guestimate displayed on the display ( could be accurate? but??) is generally default check number one when looking at any issues. And can after a full charge be a very good indicator of the battery status.

@D8veh I opened the connector and above were the results of what the wires were connected to. See attached pictures. What do I need to do to check with a multimeter? How do I check the battery and charger wires voltage and polarity?

Thanks too @thelarkbox

Edited 3 hours ago3 hr by urbanCyclist

The meter has two probes that are black and red. If they have sockets in the meter that they plug into, make sure that they are plugged into the right ones, which will also be black and red. Set the meter to measure DC voltage. Sometimes, when you have a big dial-type selector on the front of the meter, the voltage is divided up 0v to 20v, 0v to 200v, etc. Choose the 0 to 200v.

With the charger switched on, put the red probe on the brown wire and the black wire on the blue one. If the brown wire is the positive, there will be no minus sign in front of the reading. If the brown is the negative, there will be a "-" in front of the result, like -42.0v.

Be careful not to let the two probes touch each other while touching the wires because it will blow the fuse.