Yeah, you could go that way, too. As long as there's something to keep them topped up be it total isolation (my intention) or constant-charging (your suggestion), you're good.
I'm planning to run them without a BMS for now, see how they go as is. Ned and Cam told me I should put an active BMS on there as they draw micro amps and won't hurt the longevity between car uses. I'll have to run the math, they are only 8AH capacity which isn't much.
I know from experience with my jump pack pictured above that it'll crank the hotel around in gear with a totally dead lead acid for a significant period of time before the alarm goes beeping, maybe about a minute. I'm more worried about starter overheating than killing the jump pack. It's also 8AH, same chemistry, but rectangular/flat cells (had it open the other day).
What I mean by that is, if the car is in good health it'd probably start fine with 1/4 capacity in the battery due to the voltage profile of them and low internal resistance.
Good point re caps, though, I should run something in parallel with them to absorb high frequency ignition voltages and prevent micro damage from brief high voltage spikes.
The cool thing is they're $17 each from
https://evassemble.com/ and come with the plastic end caps to suit the number you buy. I got 8 + a 6A charger as pictured to pre-charge them.
Going to run a datalogged LeadAcid vs Headway38120HP4S test on the 240 sedan to gauge performance / capacity to start a moderately high compression 2.3l engine.
Stay tuned :-) Maybe I should fork this into a thread of its own in pit lane and link back to that from here. Might just do that. Maybe tonight.
