"New" battery not working with my Bafang mid-drive- help?

[broombroom]

HI everyone, I have a 36v Bafang middrive i bought secondhand. It has a DPC 18 display, and a battery of unknown size. (doesnt say on it). I have had it for 3 years and its been going great. The battery is not as big as I'd like however.

I bought a 36v 10.4ah battery off facebook marketplace for $70aud. It was a second battery for a bike that was stolen, it came with charger and a weird proprietary plug. The owner didnt know what condidtion it was in had been in the shed for a while. I opened it up and bypassed the propriatary plug which may be part of the problem.

When I use my voltmeter it says the new battery voltage is 42v
But when I plug the battery into the middrive the bafang says the voltage is 24v??!
The bafaang won't even attempt to use the battery as presumably it is below the low voltage safety cutoff.

What is going on, any advice here?
Any way to capacity test the battery so I can see if the battery can handle the load?
Thanks any advice will be much appreciated.

 

[docw009]

Does your meter also say 24V when the DPC 18 says 24?

Australia is 240 volts so your appliances may be too heavy duty, but I often use a 110VAC hairdryer to take a little power out of an ebike battery. You might try a load test with a toaster or other appliance, I think though that your bafang is telling you the truth,