I did some research, but didn't find the exact situation.
I have a device that has a battery inside and is powered by a 5V 4000mA USB-C charger. The device requires the battery to be connected at all times and won't turn on if the charge is less than 5%. The device is constantly connected to the charger when in use anyway, but it simply requires the presence of a battery.
The original battery was 3.7V 6200mAh 22.92Wh flat Lipo pack, made of 2 parallel 3100mAh batteries connected to a protection circuit.
I only found 2 batteries of the same size:
1; 3.7V 6600mAh LiIon pack made of 3 parallel round batteries 2200mAh each
2; 3.7V 3000mAh LiIon pack made of 2 parallel flat batteries 1500mAh each
Even though the device is connected to the charger, it still drains the battery while in use and when turned off it takes around 20 - 30minutes to recharge. So I suppose the battery is somehow used alongside the charger. Is it safe to use any of these 2 battery packs?