I rarely use it, would like to have it just in case. From my understanding sla batteries are a bit more high maintenance in regards to charging intervals. I'd like a smaller lithium unit but I'm uncertain if they're worth the added cost.
If I'm looking at 20/22ah sla units, what would be the equivalent lithium unit? 20000mah? Or is it on a different "scale".
For "just in case", why do you think you need it? Just keep jumper cables in your vehicle.
SLA means "Sealed Lead Acid" which doesn't automatically mean AGM. All AGM batteries are SLA, but not all SLA batteries are AGM's. Like squares vs. rectangles.
They're just sealed so they don't spill and leak if you tip the jumper box over.
As far as charging, they're the same as all other lead-acid type batteries. Usually, the packs don't have good internal charging circuits. They're pretty basic, with set charging voltage and current. Like a laptop or cellphone, you don't want to leave it plugged in all the time or it will ruin the battery.
Often times, you can tell when somebody brought a pack in if they left it plugged in 24/7. The battery swells and bulges.
If you do choose to replace the battery, get a Christmas light timer and set your boost pack to only charge 4-8 hours a day (in order to maintain it).
If I was you, I would not get any sort of boost pack at all, here's why:
1. Just keep jumper cables in your trunk. If your battery dies when you're at the store, you won't have the jump pack anyways (unless you carry it around all the time in your vehicle). Find someone to jump you for free.
2. If it won't start at your house, jump it with your wife/girlfriend's vehicle or a neighbor's. If you live alone and are antisocial, get a battery charger with a "boost/jump" setting around 200 amps. If you invested your money in a good battery charger instead of a boost pack, you can trickle charge your battery when it's not in use to increase its life, as well as jump your vehicle when the battery does go bad.
3. I've got more reasons, but I feel like I've already typed a book and am now just ranting. If you want to know more still, I can add more to this thread or PM you.
CLIFS:
1. Don't get a lithium boost pack or replace your battery.
2. Keep jumper cables in your vehicle.
3. Invest in a good battery charger with trickle and jump settings instead.