Auto electrical advice required

Doing this will cause your batteries to become unequal in charge and the drawn battery will stay flat while the other will recieve too much charge. you will reduce the life of you batteries considerably as well as having starting problems. Another reducer is the best option and only costs the price of the battery you will damage by drawing off it.

The easiest and most reliable way is to fit a Redarc Charge Equaliser, you can then pull any amount of 12v from either battery and it keeps them both at the same potential. No loss or wasted power through stepdown transformers either. also no restriction on power drain on 12v.
Think of two water tanks with a pipe between the bottom of both, any water removed from one will be topped up by the other through the equalising pipe.
I've had one fitted for over 4 years on my 24v vehicle with zero probs, actually just replaced the batteries as one dropped a cell, they were 4 years old.
No connection to Redarc just a satisfied customer.

Need to have charge equalizer fitted or will always have trouble and be replacing batteries every 12months to 2 years.
Cheers
Charlie

I used this system for many years without problems except that if your first battery does fail or go flat you could get reverse polarity through the equipment you have connected to the first battery. use a one way diode in the + wire

bob

Thanks guys for your input. Obviously when using the caravan via the stepdown transformer and or the engel hooked to battery 2 it will help the situation. For now I will swap the batteries over every few months.

whenever you have two batteries in series they must be of the same potential to be charged correctly and prolong the life of the batteries. Once you drain one it will not automatically come back up to the same level as the charged battery. The same amount of charge goes through both batteries so one will always be more charged than the other. If you only have a uhf or some such drawing you may get lucky and still get reasonable life, but only maybe. Also any auto electrician who puts a new battery in series with an old one is decieving the customer because its life will be cut drastically. The only way to do this is to fit another reducer or as above fit a charge equiliser both will work ok. Swapping the batteries around wont work unless you take them out on a regular basis and charge them both to the same level. If you dont fit a reducer or charge equiliser you will have more problems than it is worth.

When drawing 12volt off one battery that battery will be low charged on 24volt system. When engine is running alt will bring batteries up to required surface charge and regulator will turn charge off. Equals one battery with surface charge of 13.8volt and one battery fully charged of 13.8volts. When starting vehicle on 24volt one battery fully charged and one partly charged, resulting in battery overload, poor voltage to starter motor ect ect ect. Charge equalizer only way to go.
Cheers
Charlie Milton