David, I've owned batteries with fold out/flap handles. If yours does not have these then the idea of a couple of straps is a good one. Can you make 4 wedges to tap underneath the battery and slide a couple of webbing straps underneath. I suppose a couple of trouser belts would do the job and you could then buckle them up and feed a broom handle through so two could try and lift instead of just you.
Colin