By "auto jack" I presume you mean an electric tongue jack? Many have done it by running #10 wires forward from the battery in the rear compartment.
Adding a second battery on the tongue, and wiring it in parallel with the existing battery in the back, can be somewhat counter-productive. The problem is that the tongue battery will tend to hog most of the charge current that is coming from the tow vehicle while you are driving, leaving too little to fully charge the rear battery. And the same thing will work in reverse when you are operating on shore power. The rear battery will tend to hog most of the charge current from the TM's built-in charger, starving the front battery. This happens because of the voltage drop as current flows through the long wire leading from one to the other - the two batteries do not have quite the same voltage. This doesn't mean that the farthest battery will not charge at all - but it will be slower, because the battery nearest the charge source will have a somewhat higher voltage, which will signal the charging source to shut down before the far battery is fully charged.
If you do decide to add a front battery, and connect it in parallel with the rear battery, remember that you will need to include a fuse on both ends of the interconnecting line. If the connecting line develops a short to ground, you have to isolate both batteries from the fault.
Whew! Did that make more sense than it felt like?
Bill
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