mAh = Milliamp Hours. The difference is how long the battery can be expected to last. Getting a higher number than the original should mean that the battery will last longer than your previous one did, assuming both are new. It does not mean the battery is incompatible with your laptop.
My original Dell battery type U4873 Only lists 11.1 Volts same as replacement from amazon ML:G450 no info regarding mAh are written on original. This the only info regarding your question I can offer. Listing for replacement through amazon stated my computer model as known comp. for battery cell replacement. Hope this helps.