Was at a car show and someone used a portable jump box to start a car. It was 600A peak and 300A cranking. I am looking to get one and it's the NOCO Boost Plus GB40. It's 1000A, but not sure if that is peak or cranking. I have a Stanly 1000A peak 500 A starting one in the car currently and it has an air compressor on it. I may keep that as well just in case. The Stanly has to be charged with an electrical cord. I admit, I forget to charge it and tried to use it to jump someone and it didn't have enough juice. The portable ones have a USB charging port and can be charged on the way to an event to make sure it's good to go or in the daily for winters. Easier to remember to charge it. Is the NOCO GB40 a good one for starting a vehicle up to say a 440ci engine?

The other question is about voltage when starting. My car doesn't have a voltage gauge so I put a plug in one for the cigarette lighter. It measures good when the car turns on (12 or so volts) and charging (14 or so volts) as well. I noticed the other day when I was starting it, the plug measured 8.7 volts for a split second. I never noticed it before, never really paid attention I guess, but is that amount of voltage dropping to start the car normal?

Depending on how old, What CCA, Current charge, Temperature will effect how a battery performs. If the battery is able to keep a charge you shouldn't need a jump box. If you don't run your car for long periods look into getting a battery tender it will keep the battery charged.

My battery keeps a charge and has a battery disconnect on it. Not a fan of a battery tender when not at home. I believe the CCA is 800. I am considering a jump box in case I am at a show and need a jump or if someone else does. Never hurts to have one. I carry cables, but sometimes you play heck getting to a spot to hook them up.

Remember: when you're jump starting a car with a dead, or weak battery, some of the power from the jump box
will be diverted to the battery. Thus less power going to the starter.

I would not rely on that reading as most accessory circuits are bypassed when in the start position. In addition the cigarette lighter could cause a Voltage drop due to it's distance from the battery. Ifyou want an accurate reading it would be best taken at the battery posts