The good news is that it is pretty hard to go wrong picking out a battery.

The basic choice is a Group 1 lead-acid battery - the original equipment battery. A typical battery is this one:

https://www.autozone.com/batteries-s...cca/960195_0_0

Auto Zone, O'Reily's, Rural King, NAPA - there are vendors all over the place. I've had a Group 1 lead-acid battery in the '48 since its rebirth and unless I do something stupid like leave a light on, it has never unexpectedly run down or failed to crank the engine - even in really cold weather. These typically have a 1-year warranty, but you can find 3-year or so if you're willing to shell out the bucks.

But, if you want to go to the next level, an Aggregate Glass Mat (AGM) battery is the next step.

https://www.autozone.com/batteries-s...cca/437833_0_0

It is a different form factor, so securing it in place is a bit of a challenge, but it gives more cranking amps, something that might be an advantage if you have either a new, tight engine or a worn one that needs to spin for a while to get it going. They're more expensive that the Group 1 batteries, but they typically are warrantied for 3-years.

As the old guy says; "You pays your money and you takes your choice".

Probably more important that battery choice is paying attention to the starting and charging system on a 6-volt Jeep. When you start out with only 6-volts, every tenth of a volt is previous.

Make sure terminals and connections are clean and tight. Don't scrimp on battery or starter cables; 12-volt #4 AWG parts store cables won't get the job done. KWAS uses #1 AWG for their cables and they are a minimum size.

https://www.kaiserwillys.com/battery...66-jeep-willys

If you can find them, braided welding cables make an even better solution, but you usually have to get a good auto electrical shop to crimp on the terminals.

We have seen a number of folks having starting issues where it turns out the actual starter switch on the push-in starters is the issue. They get old, dirty and pitted, so don’t overlook that switch. Starter bearings, bushings and brushes also slow down starters and increase current draw.

I know – more than you asked for, but we’re kind of like that insurance guy on TV; We’ve seen just about everything – but there is always something new coming.