With our JrFuel car I'm always looking to save weight, because the rules are 3.5 lbs/ ci, with driver. So we use a remote battery pack, plug-in, prime the injectors, start the car un-plug, head for the water-box. I do use an on-board Lithium-ion light weight 12 amp battery [ one lb] to power the transbrake and RacePak computer. I discovered this one pound battery when we were setting up the chassis for the all iron early Hemi, and looking to cut some weight. We saved 6 pounds by using the Lithium-ion battery, we only charge the battery at the shop, not at the track. Since the battery worked so good for 4 years, I made a remote Lithium-ion battery pack [ two 12 volt batteries in series ] for starting the engine. We need 24 volts to start my 16;1 compression SBC or Hemi, and spin the 20 amp MSD mag fast enough.
The remote start pack weights, with carry case and cables just under 10 lbs [ my crew loves me]. We only charge at the the track after we are done running for the day if we are starting the motor allot looking for some issue.
If you want to see what the remote battery pack looks like check-out my Haydenent.com site. Now if you want to have the option of on-board battery for starting, just keep in mind the 24 volt system only weighs less than 10 #.
As far as battery placement, put it up front if you need or have ballast on the front end, if not put it under the rear-end for more bite.
I have most guys don't carry enough weight on the front end. I have told guys with problems with the car not going straight to add 20 lb to the front and they went quicker/ faster. Most older dragsters have the motor close to the rear-end [ 36-38"] that's from the rear motor plate to the center of the axles. They were built that way before VHT, looking for more traction. Now some guys have trouble with wheelies, with the older style chassis designs.
Our JrFueler has a motor location of 48" since 1997.
Jon