Hi Tom,

Tony is right on the money. Most guys run two batteries either to add running time or because there are two connectors that need to be fed power. Some lack or prefer not to use a Y connector to unify or eliminate the two batteries. There are advantages and disadvantages to using one battery for the DMD/ESC and one for the MF/sound boards. The 7.2 volt hobby battery has endless variants. I'm running 4500 & 6800s NiMh now but when I started a 2200 NiCad was the big thing and didn't last long at all in a battle and developed a "memory". Think of the battery as a sponge. How much will it hold and how long will it take to re-charge. High amp batts. have higher quality/capacity cells that are matched to each other. Many of the stock H L 1700s etc.... were useless upon delivery. Heat is the enemy of all things electric and batteries will need to be cooled before and after charging or discharging. I frequently station a fan next to my charging area at Danville for this purpose. The stock HL charger will charge a 7.2 batt. but the higher the "sponge" capacity the longer it will take. DO NOT overheat the batt. or forget you're are charging it. You will fry the battery. I have two Onyx chargers (a single and a dual battery). With the dual you will be able to charge them faster than you can use them. Spend a little more and get a good unit with a cooling fan and full charge alarm. The link Tony sent is for two good batteries but the charger is cheap and not practical.
Here is a link to the Onyx but shop around for deals...http://www.amazon.com/Onyx-Dual-NiCd.../dp/B001DTULS8

Losing a battle because of a dead battery is just like a tank running out of fuel on the field. It is very aggravating. I once ran a great head to head battle with my Jagdtiger vs. Mike's KT after he had a respawn/tank recovery. The size and extra weight of my JT ran down duing the hour long battle. We were in our death throws when my battery (I only ran one 4500 batt. back then) ran out and he won. We both regreted the anti-climatic ending and were disappointed. It was just like the real thing. Thats why many JTs were surrendered intact after the war. They were hard to kill and/or ran out of fuel. I recently ran one new 6800 in my Tamiya Panther for over four hours of on/off battles (continious running time would be about 2 1/2 hours) at our recent NEAD battleday this past Sunday. If weight and space is not an issue you can run two batts. But one good high capacity will serve you better and reduce "down time". I have many batteries and share them with my girls at the battles. We use a very simple system to keep track of what is charges and ready and what is used. A small rubber band rolled towards the connector when fully charged and rolled away is used and awaiting a charge.

I hope this helps. The highest quality batteries are a waste if the charger is not up to the task. Get a good fully automatic smart charger first and then one or two high capacity batteries that will keep you battle ready. I use the H L low capacity batteries for testing and workbench tasks or give them away to new tankers to foster good will.

Good luck, Bob thecommandernj