Wow, it’s amazing that Gabriel Sowrian got three down-votes, when his answer is absolutely correct and on-point. Thumbs-up from me.
Andrea, you really need to learn the phonemes of English ASAP. Just listening will not be effective until you take the time to learn the phonemes, because you need to know what you’re listening for, and how to make the sounds with your articulatory organs. We’re only talking about (in most cases) a couple of hours of your time to get it right now, and then everything will be much easier. It’s more efficient to do so before you’ve learned 10000 words with inaccurate pronunciation, but still, it’s never too late.
That said, here are some tips: In most accents, the vowel in “batter” is a front vowel similar to Italian è (well, between è and a), and the one in “butter” is a back vowel closer to Italian ò (actually, between ò and a, with your mouth a bit more closed than for A, and your lips not as rounded as for ò). The recordings in the Cambridge Dictionary sound perfectly standard, and there’s almost no difference in those words between the American (the one in the dictionary sounds like it’s from the western part of the US) and RP pronunciation of the vowels.
Certainly, if you can get feedback in real time from someone who knows how to teach this, you’ll master it much more quickly. Or you can just continue fruitless hours of listening for the next couple of decades….