Steve, The amp rating is designed and should be sized based on the maximum amperage that might go through the shut if everything were on and functioning. For that you would need to calculate the potential amperage based on everything connected to it. 500 amps is a lot, but don't confuse it with the amp hours for your battery bank or amp hours used. This would not affect the size of the shunt. Hope this helps a bit. Chuck To follow our adventures, go to http://trawler-beach-house.blogspot.com/ http://sea-trek.blogspot.com/ --- On Sat, 3/28/09, StWillett@aol.com <StWillett@aol.com> wrote: I am getting ready to order a Xantrex Linklite battery monitor, I'll be connecting it to the main bank which is 2 8D batteries serving house and main engine start functions. since it can monitor 2 banks I'll hook it up to the generator start battery also. The unit comes with a 500 amp shunt, I see other shunt capacities are available. I am not sure how the 500 amp rating is determined or if the 500 amp size supplied will be ok for my application. I am not on the boat now so don't know the exact ratings of the 8D's. The product description mentions " a new shunt selection is available to measure currents up to 1000 amps respectively" When the 8 D's die I 'll probably go to golfcart batteries and add a separate main engine start battery (group 31 size) which I will then monitor instead of the genset battery. The boat is equipped with 12V windlass and bow thruster, no inverter. So, my question is, will the standard 500 amp shunt suffice for the above application? Thanks for your help and suggestions, Steve Willett