My existing bait tank has a Rule 500 gph pump which draws 1.9 amps at 12 volt and 2.5 at 13.6 volts. Thinking about using a 800 gph which draws 2.9 amps at 12v and 4 at 13.6 v.
Is there a problem with going to a bigger pump and does the amp draw make a big difference?

Other than obviously draining your battery a little quicker, the only other negative I see about a pump that uses more power is that more power means more heat so if your pump is in the tank with your bait, it might heat the water up a little more. I know that people are concerned with this for their aquaponics fish tanks, but I don't think its gonna be a big deal in a bait tank.

I just bought a group 27 deep cycle battery from Walmart and it has 109AH of energy storage. Assuming most deep cycle batteries of that size hold a similar amount of energy, you could run your new pump for around 30 hours straight if that was the only thing plugged in to that battery as opposed to about 45 hours with the old pump.

I would only be concerned if you are using the same battery for starting and accessories, I bought that battery I just mentioned as my bait tank battery.

Thanks