24V battery running 18V

I want to know If i can use a 24V lead acid/deep cycle battery, but only charge it using 20V so i can run a 18V device with it. I cannot find any 18v battery's except ones for drills, and i need a minimum of 10amps of output.

A 24V lead-acid battery is dead if its voltage is only 24V. It is 25.2V when fully charged. If you use something to reduce the voltage to only 20V then the "something" will be very hot dissipating 52W.

Maybe somebody can design a PWM circuit for you.

Well that would be great if someone could design me one, if it wont cost much to build, or if someone could point to someplace that has a 18v battery.

A 24 v lead acid at 24.00 vdc unloaded 'rested' for a couple of hours is not dead but it only has about 40% rated capacity left.

At about 2.1 vdc per cell a 24 vdc lead acid battery has 12 series connected cells. It is not uncommon for a cell to go bad and short out resulting in drops of 2.1 vdc increments to terminal voltage.

You must keep a lead acid charged. Discharging takes lead from plates and sulfuric acid from electrolyte and turned them into lead sulfate on the plates and water in the electrolyte. Charging reverses the process.

Lead sulfate starts out as a soft paste but if left on plates for a month or two it will begin to crystalize. When the lead sulfate crystalizes it will not breakdown, back to lead and sulfuric acid when battery is charged. Result is battery with less capacity.

15 NiCad or NiMH batteries in series will give you the 18 vdc. (about 1.25 vdc per cell) This is what is in the electric drill battery pack, typically sub-C (SC) size.

How about using 3 6V SLAs in series. As long as they are well matched (all new, all the same AH capacity) then this will give you a nominal 18V (18.9 V fully-charged, 17.25V end of discharge)