Easy thing to do, but in my battery there isn't any markings or on the motherboard or its manual to show if it needs and 210 mAh or 220 mAh battery. Or does it really matter and manufacturer is using terror tactics as it threatens with explosion to sell me a certain type of battery?
Well explosions after battery change are known as the prime reason for PC servicing related accidents.
mAh doesn't matter at all, higher just means the battery can store more power so just make sure it's a decent number.
Voltage is the real question, but PCs had this standardized while dinosaurs still walked the earth, unless you are running some crazy alien tech you can pop out the battery from an old PC and it will work just the same, or go to a computer shop and ask for one.