Shorai definitely. That model is good or the LFX14A5-BS12 -- fits right into the existing holder.
If size/concealment is your goal, you may go with the smaller A1 form factor (LFX18A1-BS12). It is pricier, but smaller and has more cold cranking amps and amp hours. Note: it is OVERKILL for the demands of the 550, but if you want something tiny, it's a great battery.