Battery talk
 

So, I bought a '97 Civic to replace my Echo. Battery is weak. Ironically, I'd just bought a battery (a good one, no less) for the Echo, but it won't fit in the Honda's little group 51 slot. So, that's a sunk cost.

I've heard about some of these lighter weight alternatives to lead-acid batteries, and I'd like to start educating myself before I need one for the winter. Point me in the right direction?

Braille makes light-weight batteries. Your choice of chemistry. https://www.braillebattery.com/

There are other/no-name brands of 12v lithium car batteries. Just make sure you educate yourself as to their winter performance and their reserve capacity.

There's also super-capacitor starting-aids for starting off of small batteries.

Google and possibly ecomodder search are where I'd start, now that you know what to search for.

With a little elbow grease you can probably make it fit.

If your cheap I use a $15 lawn tractor battery in several of my cars, you need to replace it more often but still cheaper than the correct battery long term.

Winter isn't bad in East Texas. Lows in the 30s and 40s with occasional stints in the teens and 20s. More important is the fact (shoulda mentioned this) as a trucker, it's parked for a month at a time, though as a matter of course I disconnect the battery when it's parked.

I know little about battery chemistry and its properties, advantages, and disadvantages.

Spend a few extra bucks and install a battery disconnect to take some of the hassle out of reconnecting the battery. Pop the hood <twist> drop the hood.

Eh. 10mm socket on a ratchet isn't a big deal. But I like the idea of potentially longer life along with less weight over the front of my front wheel drive car.

Leave it connected after adding a solar trickle charger?

LiFePO4 batteries suck in the cold and if you charge them while they are below +20°F they are permanently damaged to the tune of a 20% capacity loss.
Also under hood temperatures can damage them.
They should be located away from the engine compartment heat.
I relocated mine to inside the vehicle and put them on a forklift quick disconnect so I can take them in on cold nights

Still looking around. The temperature thing is a bit concerning. Weather here is unpredictable enough that it could get that cold, and in summer it can definitely get hot.

Starting to get a tiny bit discouraged. The Civic I bought is so clean that I'd feel bad messing with terminal ends, etc.

Fleet farm has plug in / bolt on battery adapters of all types along with knob style battery disconnects

I would still go for the $15 battery, given your circumstances even a lithium battery could overdischarge becoming an overpriced boat anchor, Franks solar trickle charger idea is a good one

For a 4 banger the little lawn and garden batteries pack a punch

Good luck