It's not a cable it is your battery vent hose. It fits in the hole on the edge of your battery (right by the red edged sticker ). It appears to have snapped so you will need a new right angle connector and get the bit out of your battery case to allow you to fit it.
I've found that a fish tank air pipe connection works perfectly :wink:
The replacement battery I bought for my E85 had 2 vents, so used the above to connect them up
Just checked my box of bits and bobs, but I've none left.
IIRC the fitting was slightly too large for the vent hole, but soon rubbed down to fit (and glued in)
I then used new air tube (as used in Tropical fish tanks) to route out of the boot
If you have a Pets at Home or similar nearby, just look for air stone/pump fittings (tee's and right-angles) - normally blue or green and a roll of air tube
They will only be pence I expect