A pump will run at just over 11V if you use cold water and continue to for ages if the split charger put a little amount back in the battery from driving,sounds like a bad battery you are only running a 12v pump they draw as much as a bloke with no arms.
Two pumps and two electric reels
As P&F says, you need a combo battery - a leisure battery class 2 that also has a CCA rating.
If you are winding in 2 electric hose reels at the same time a standard leisure battery isn't designed to pump out 40 to 50 amps, even if it is for a short duration. You will 'kill' it.
I have a diesel heater running along with 2 pumps. After a hard day and the run home I have a deficit of 13 to 15% of my 105 amp battery capacity. I have to put the charger on every night to fully recharge my battery for the next day.
Running 2 electric hose reels I might even be tempted to look at a 100amp plus starter battery.