I haven't tried one of those jump packs for starting a vehicle but they have a large amount of stored power. I have used a Ryobi battery converted to power up a 20w mobile device (need to find that thread from last month).
I should add, we have good coverage with no repeater with both the Midlands and the Baofengs.
We’re in a pretty heavily wooded area with rolling hills.
I hear that you want to buy once, but at 20 acres you should be able to get coverage across the entire property with a pretty simple set up. We started with a couple of the Midland upper tier bubble pack GMRS radios on a larger property.
We’re still just using some Baoefeng GM-15PRO and getting excellent results.
Start by just adding the input tone for the repeater you’re using on the frequency of the repeater (ie channel 20, 21, 22,…). Don’t change anything else.
You are still limited to the GMRS frequencies for TX. You can add a different tone to get into a repeater. If you have more than one repeater (in say a different location) you could put that into the DIY section (above channel 31).
Above 30 are the DIY channels. You can set them up to TX to a repeater but they will still only go to the same GMRS frequencies.
You can also set up some of those empty “channels” to RX in the VHF and ham UHF bands. I left a gap and started at 101 and put in several VHF and UHF frequencies to RX only. Comes in handy when scanning channels (instead of entire frequency spectrum).