I recently saw a game where white avoided the mainline Berlin wall defence to the ruy lopez with Ba4 after Nd6, white went on to lose the game, but the position seemed at least equal in the opening. 

Black seems to have two main options, e5 or exd4, both met with Re1, Be7. Anyway, is this any good? 

i've not seen that particular variation before, according to my engine it is not any improvement on Bxc6, although it does circumscribe trading too much material off the board too early in the game. In the tutorial I was watching on this opening another way for white to play is 6.dxe5 Nxb5 7.a4

Instead of 4.0-0 it is possible instead for white to play 4.d3. Black can then try and spring the "Mortimer trap" but if white knows what he is doing then they won't be experiencing any problems.

Oh, 6.dxe5 Nxb5 7.a4 is very nasty. :)

I recently played that one, white was pushing his king side and it was not so easy for me: 

it's worth noting and i forgot to mention in the OP that this is a pawn sac, but black can forcibly be given doubled pawns, yes though the point is that there isn't as much trading as in the mainline so white (or indeed black) can try for a win. another alternative to attempt to keep more pieces on the board is 5. Re1 which i have played some, but the position ends up symmetrical and black is likely to know some theory for this if they play 3..Nf6 in the first place. 

6 Ba4 is a rarely seen line, its main advantage is to take Black out of his preparation, if any.  Either ...exd4 or ...e4 seems perfectly playable.

If you don't like the Berlin, you can also try  3 ...a6  4 Ba4 Nf6  5 0-0 Bc5.  White scores fairly well at the master level, but it isn't as well known a line, and at amateur levels is quite viable.  Or 5 ...b5  6 Bb3 Bb7 is interesting, too.

You can always try an early d3 system.

Overall, it is a neat trick for black to pull on white.

1.d4

Why doesn't everyone know about 4.d3, when they talk about the Berlin?

It is like people are complaining about the Berlin when they don't even understand what's going on in it and are being passive and submissive about who's opening recommendation to play. Ffs, the Berlin isn't so bad for White. You can gain a lot of interesting knowledge from it. No need to avoid it for such trivial reasons---> do you even know why you avoid it? 

Okay, so 4.d3 is the most common way to approach some anti-berlin.

Did I mention 3.d4 is also a nice anti-berlin?

whoa, forgot about this thread, update: did eventually settle on 4.d3. I didn't like it at first because it seemed to waste a tempo, however this tempo is made up for by not necessarily having to play h3. I realize the berlin does have a lot of learning value, I simply did not enjoy the types of positions that came out of it. And enjoying the games is in fact the reason i play ;). The line i asked about in the OP ended up being too easy for black to play, being able to just return the pawn whenever necessary with a solid position.