Beatles album with most covers?

By the late summer of 1964, the Lennon & McCartney song factory was running low on stock for the new album due before Christmas. Trapped in an exhausting touring and recording schedule, they lacked the time and the energy to create high quality new material.

"They were rather war weary during Beatles for Sale...they'd been battered like mad throughout 1964, and much of 1963. Success is a wonderful thing but it is very, very tiring." George Martin

That wearniness is apparent in the bleak record sleeve The formerly buoyant band members appear to be dressed for a winter funeral and stare unsmiling at the camera. They may be 'for sale' but don't appear happy about it.

Weariness is alsoe evident in the titles of the new songs (Baby's in Black, I'm a Loser, I Don't Want to Spoil the Party etc) reflect this as does that of LP: Beatles For Sale. 

Covers

Basically it was our stage show, with some new [original] songs. Paul McCartney

What Paul later conceded, was not the official line at the time Beatles for Sales was released in the UK.  A contemporary review in the NME was more on message:

There are 14 tracks, including eight new Lennon-McCartney compositions. Numbers by Chuck Berry, Carl Perkins, Buddy Holly and the Lieber-Stoller team complete the composing. These non-Beatles tracks .... reflect the early years of the group because they were mostly numbers that raised screams at the Cavern club in Liverpool. Nowadays, the Beatles don't get much chance to play them...... NME Review 

Back to the future

After Beatles For Sale The Beatles reaffirmed their commitment to releasing only original material,  Effectively ending live performance gave them more time for composition and in practical terms they no longer had a live set to draw on for 'numbers that raised screams'.

Snatches of old favourites did punch through - most notably on Let it Be where the traditional tune Maggie Mae is given a quick run through. And arguably John Lennon provided a de facto cover of Chuck Berry's You Can't Catch Me - something Berry's lawyers pointed out forcefully. They would be placated by new credits on Lennon's later solo LP, Rock and Roll dedicated to the songs of his childhood.