can I charge a cranking battery on any battery charger or dose it have to be a cranking battery chager?

most any charger will work, I would keep it between 6 and 15 amps.

thanks for all your help Ben. I got a nother qustion for ya my gauge on my dash says im runing 12 volts is that enuff volts or do I need to charge it or dose it very for each motor if it helps I got a 2003 mercury 90 hp ELPTO. agin Ben thanks for your help.

i think it should say 12 cause its a twelve volt battery   your motor has an alternater that charges it each time its running    your trolling battery should always be re charged if your cranking battery isnt holding a charge   something could be wrong with the battery

I should be reading higher than 12V.  A fully charged battery will have 12.6 - 12.8 volts.  With the motor running at approx 2,000 rpm it should be showing somewhere between 13.8 - 15 volts.   I don't put a lot of faith in the dash quage and use a good digital multimeter across the battery terminals to check it.  I also strongly recommend charging the cranking battery when you charge the TM batteries.  Normally the motor is not run enough during the day (unless you're making long runs) to keep the cranking battery fully charged if you're running the livewells pumps and electronics.

To check the charging system, connect a digital volt meter across the battery and note the reading, crank the motor and bring rpm up to about 2,000 and note the reading, if it did not increase, you have a problem with your charging system.  Bad batteries are the number on cause of burned out charging systems.