I'm telling ya lithium polymer (lipo) is the way to go , great in price and performance. They can handle the current demands without voltage sag that causes ezb to disconnect.

Large capacity battery 5000mah http://hobbyking.com/hobbyking/store/__9172__Turnigy_5000mAh_2S_20C_Lipo_Pack.html

Ok. They will be able to power 2 hbridges and the ez-b?

Thanks for all the help by the way.

I use a 5000mAh in Melvin and it copes very well, and lasts a long time. I will be using the same in Jarvis.

There will be no problem powering 2 hbridges and the EZ-B (provided you don't throw on 4 extremely large big motors).

ill just be using the motors in the arms and the tracks on the motor controllers. how long do those 5000mah lipo's last?

5 amps for 1 hour, 1 amp for 5 hours, 500mA for 10 hours. It depends on what's running. Add up the current draw of each thing on the robot, convert to amps if it's in mA (just multiply by 1000 for anyone who doesn't know that) and divide 5 by that number and that's how many hours it'll run on full load.

If it isn't moving all the time then it can be greatly reduced as the motors are no doubt the biggest current draw.

the arms will only be used every so often. theres one power saving area.

Melvin runs for hours on one charge. In fact, it has been at least a month since I last charged him (a lot of that time he has been off but I have also done a lot with the LCD and script testing, sneezing, sleeping, blinking etc.)

However, one thing you need to be aware of is that LiPo batteries do not like undervoltage, i.e. if it drops below 3v per cell the battery wont charge again. It's a good idea to add in a LiPo monitor circuit & script and possibly an auto cutoff.

that's what I don't like about lipo batteries. they require a fair bit of safety.