Vers 1Q bluetooth speaker. replaced battery, squealing sound problem

Hi repairers,

I have this Vers 1Q bluetooth speaker - a wooden cube thing from about 2013. I wonder if you might have some ideas, even if you're not familiar with the specific device. It's a neat little speaker, but stopped working - I thought likely the battery was spent - it wouldn't work or charge. I bought a battery on eBay - not the same shape but fits inside fine. It is 2000mAh 3.7V - as the original. On charging there is a promising red light, but then some loud high pitched noises through the speaker happen. So naturally, I unplug it. I can't see a problem inside - my connections inside are red to red, black to black. and you can't connect the little plugs to the wrong place. What would that sound suggest to you? I guess the battery must not be compatible, but are correct replacements available?

I have a better bluetooth speaker, but I'm keen to reuse this, rather than chuck it.

Many thanks

(the new battery is the one connected here)