turning 2x12v into 1x24v

scampo77 said:

because the way that i pictured this working was if i took the first 12v battery on a alternator put a diode between the positive lead and then added another battery and connected the diode to the negative lead of my new battery i could get 24 v without disrupting the original charging system. from there i could charge 24v into second battery

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you couldn't "charge" 24V into the second battery without a 24V charger or without taking the batteries out of series and putting them in parallel for charging.

And you still wouldn't need a diode to do that. a simple jumper would give you 24v across both batteries. I do not recommend you actually do any of this. if you need 24V for your light I reommend you:
(1) add 2 seperate new batteries and
(2) add some relays to :
(a.) align the 2 batteries in parallel, disconnect from the lights, and connect them to the charging system and
(b.) align the batteries in series AND DISCONNECT FROM THE CHARGING SYSTEM and switch power to the lights
when you try to have the charging system charge 1 battery out of 2 in series, you are going to run ito big problems