Battery Voltage Reading Discrepancies

Hi folks, I’m a bit stumped as to this situation. I’m working on a build, and I’m almost done.

Bustin Sporter build, with enclosure and battery from @eBoosted.
FOCBOX Unity & Haggydrive. Configured and tested, functions fine.

I didn’t have a charger until a couple of days ago, (first one I ordered didn’t work at all) and so now I’ve charged it. Charger light turns green, and I left it plugged in for another 24 hours or so for the sake of a bit of balancing. I haven’t used the pack much aside from testing, so I ran it from 40% to about 30% before getting and using the charger.

The charger is a 50.4v 4A from Torqueboards. I tested the output, it does output the 50.4v (blips a little to 50.5v once every few seconds, which most of my chargers do).

When I open the Unity app, it reads at 98%, 50.1v.

The voltage feed to the remote reads at 49.9v.

Is this all normal? I don’t think I did anything wrong…and it functions. My only concern really is balancing. If the pack is only ever going to be at 50.1v/98%, that’s fine by me so long as the charger and BMS will still balance the pack once it detects full voltage.

I had assumed the charger, being that it puts out 50.4/5v, wouldn’t turn green and shut the fan if it detected a lower voltage from the pack.

Please keep in mind that I’m new, this is my first build, and I’ve got a lot to learn…so please be gentle. I realize there’s likely something plain that I’m missing.

I appreciate your time. :pray:


I have 3 unities in use right now, not one of them gives accurate voltage to the 10th of a percent. I think this is know issue, but mostly it is not worried about too much.

If you want to verify the balance value of the pack, measure the voltage at each group via the balance lead and the pack negative.


One of my chargers only charges to 98% as well. Do you know if it’s a float or trickle charge?


I have two VESC 6 and two FOCBOX 1.3 on my bench right now, and all 4 read different voltages, but one of the FOCBOX 1.3 (VESC-X) reads a full 3.0 volts low. That’s all connected to the same battery.

A lot of the components used in electronic manufacturing have a 10%, 5%, or 1% manufacturing tolerance on their resistance/capacitance/voltage values, and these errors can manifest down the line as different voltage readings.

If stuff is within a few percent, it’s fiiiiiine. 49.9V is within 1% of 50.4V


This can be found by measuring the output voltage. If it’s contant 50.4 it’s probably a trickle charger. If it turns on and off endlessly (while not connected to a battery), it’s probably a float charger. Trickle chargers will balance a pack faster but float chargers are better to keep plugged in all the time. Trickle are better to unplug a few hours after full charge is achieved.


I don’t know for certain, but given what’s been said here I assume it’s a trickle charger. I don’t have one of those gauges, but I can make one to see about the charge type.

I’ve only measured it with my multimeter and it seems to be a constant 50.4/.5v.

Thank you all for your input, that sets my mind at ease.

So for the sake of balancing, would it be best to leave it plugged for only a few hours after green lighting? I’ve often left a board on for extended periods of time to make sure the pack is balanced. But that’s only ever been on non-DIY things.


A lot of the balancing occurs at full charge so as long as your bms isn’t getting crazy hot and you’re riding regularly, it isn’t a problem to leave it plugged. Leaving it plugged for a few hours after going green is a good idea.


Your multimeter probably isnt super accurate either, especially in the millivolt range on a 50V reading But probably closest of them all.

All depends on the resolution of the device and how well its calibrated.
Does the untiy have a calibration per individual unit after fabrication? No.
Does the vesc6? No.
Does your BMS/PSU, probably to some degree. Atleast there should be a QC variable.

Your most accurate source in all your meassurements is probably your multimeter, which in itself need a yearly calibration to be keep beeing accurate.

So dont sweat it too much unless there are several volts in difference.

Sidenote: all cables introduce a voltage drop. thinner cables yield higher drop per meter, so keeping your balance cables in a smiliar length is a good idea if they end up longer then usual in your application. Atleast you’d have the same drop over all cables resulting the cells beeing at the same level even tho they might not reach 4.2V.

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