Whatever battery (or batteries) you go for, make sure it is a leisure battery. (deep cycle)
The smaller batteries are of course going to be lighter and therefore more tempting if you are using a trolley system.
So to refuce weight you can always go for a couple of batteries and change them over halfway through the day.
The only danger with that though is that you might end out running one of the batteries down too far, and if you notice your water flow lessening then you probably have.
Leisure batteries do not like to be run down, it shortens their life considerably.
I try never to risk going 2 or 3 days between recharging, I stick on the charger every night.
It's tempting to buy the cheapest battery you can find, but ultimately you get what you pay for.
Your battery is the engine for your system, shop around for the best price for the particular model you go for, but don't get it out of the bargain bucket!
Ian