How to charge a second battery while driving

[Harleyman]

I hope some of the learned members can advise me on how I can charge a second car battery while driving. I use a second battery to run a 12V to 220V converter when I take my charity car out which is an old Ford Mondeo I run a small smoke machine and LED lights. If anyone can advise it would be very much appreciated.

 

[xero50]

There's going to be a wide choice of solutions to this. That said, if it were me I'd say just get a simple charging module of the type that you would use if you were towing a caravan. (Many caravan towing kits and suzi's offer the facility to charge a caravan's batteries whilst driving). So all you would really need is a split-charge module.
This explains things much better than I can:- Split Charging Guide - caravans, campervans, motorhomes, boats, vehicles