# How to determine voltage/amps a circuit board expects

I'd like to add a new power supply to a board that came with 2xAAA batteries wired on. The issue is that the two batteries were connected on opposite ends of the board. I'd like my replacement power source to be a single battery pack or other power source and split the voltage using a jst splitter.

Open questions:

• Is this even feasible with a jst splitter?

• How much voltage/amps should I be supplying so that it matches the two AAA batteries going individually into the board.

I tried to use two AAA batteries in series to power the board but it seemed to not be enough power (or just didn't produce anything noticeable).

I have successfully made the board turn on if I attach a pack of 4xAA batteries to the board but it starts to overheat, so that isn't the answer of course.

• What's a jst splitter? Also, your circuit board probably has them on different sides for a reason. What is this board? We're going to need a lot more information than that. – Hearth Feb 4 at 23:33
• Why don't you use a cheap DMM to measure voltages between batteries, connectivity between circuits when batteries are removed, and consumed current when batteries are connected? – Ale..chenski Feb 5 at 1:30
• Good idea. Sorry I'm new to this. – art_sr Feb 5 at 1:37
• Batteries placed on different sides for wheight balance, I guess. The question is how do they connected to each other: in series, in parallel? Or they are fully independent? Use DMM in "short circuit detection" (beep) mode to reveal connections between batteries. – Eugene K Feb 5 at 7:31

I have never used that board or a JST splitter, but I am going to make a guess:

1. If the batteries are in two different places, that probably means the board has two different circuits that do not connect to each other.
2. If it overheats when both batteries are together, you are probably applying twice the needed voltage to one of the circuits and none or too little to the other.
3. Your splitter doesn't say it splits the current evenly. I assume it isn't. In order to use one battery pack, you need a circuit board that makes sure equal power goes to each side. What I would do is buy two single battery mounts and place them next to each other, then run separate wires to each side.
• Probably a good call. I was trying to keep it to one wire since I'll be threading the wires through my shirt and to my pocket, so less wires the better. – art_sr Feb 5 at 1:38