I use a heavy duty battery; the type used to power my Transit van and have no problems. I've had the same battery for about two years now and simply charge it each evening.
this is not aimed at you at all I thought I better add that first.
But people saying they use this battery and this battery really does not mean to much, you could use a 50ah battery and it be fine if you work on your own and only clean for a couple of hours, now add 2 people working 8/5 the same battery would give up.
I personally have used car batteries for 8 hours a day 2 people and they dont last and in a short time they stop holding charge, only battery that I have used to date that is man enough is a 110ah that I got with a system I bought second hand then sold.... it weighs a ton but is hassle saving.
what hours to do you guys work and with what battery ? is there just one maybe 2 or three using it. how do you charge. these answers will help others get the real story.
Ian
p.s I do not use hot on demand ( my water seems warm anyway somethis to do with the weather I guess
)